Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4307 insertions, 0 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
new file mode 100644
index 0000000000..b1ef7be120
--- /dev/null
+++ b/mm/filemap.c
@@ -0,0 +1,4307 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *	linux/mm/filemap.c
+ *
+ * Copyright (C) 1994-1999  Linus Torvalds
+ */
+
+/*
+ * This file handles the generic file mmap semantics used by
+ * most "normal" filesystems (but you don't /have/ to use this:
+ * the NFS filesystem used to do this differently, for example)
+ */
+#include <linux/export.h>
+#include <linux/compiler.h>
+#include <linux/dax.h>
+#include <linux/fs.h>
+#include <linux/sched/signal.h>
+#include <linux/uaccess.h>
+#include <linux/capability.h>
+#include <linux/kernel_stat.h>
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/syscalls.h>
+#include <linux/mman.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/uio.h>
+#include <linux/error-injection.h>
+#include <linux/hash.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+#include <linux/security.h>
+#include <linux/cpuset.h>
+#include <linux/hugetlb.h>
+#include <linux/memcontrol.h>
+#include <linux/shmem_fs.h>
+#include <linux/rmap.h>
+#include <linux/delayacct.h>
+#include <linux/psi.h>
+#include <linux/ramfs.h>
+#include <linux/page_idle.h>
+#include <linux/migrate.h>
+#include <linux/pipe_fs_i.h>
+#include <linux/splice.h>
+#include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+#include "internal.h"
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/filemap.h>
+
+/*
+ * FIXME: remove all knowledge of the buffer layer from the core VM
+ */
+#include <linux/buffer_head.h> /* for try_to_free_buffers */
+
+#include <asm/mman.h>
+
+#include "swap.h"
+
+/*
+ * Shared mappings implemented 30.11.1994. It's not fully working yet,
+ * though.
+ *
+ * Shared mappings now work. 15.8.1995  Bruno.
+ *
+ * finished 'unifying' the page and buffer cache and SMP-threaded the
+ * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
+ *
+ * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
+ */
+
+/*
+ * Lock ordering:
+ *
+ *  ->i_mmap_rwsem		(truncate_pagecache)
+ *    ->private_lock		(__free_pte->block_dirty_folio)
+ *      ->swap_lock		(exclusive_swap_page, others)
+ *        ->i_pages lock
+ *
+ *  ->i_rwsem
+ *    ->invalidate_lock		(acquired by fs in truncate path)
+ *      ->i_mmap_rwsem		(truncate->unmap_mapping_range)
+ *
+ *  ->mmap_lock
+ *    ->i_mmap_rwsem
+ *      ->page_table_lock or pte_lock	(various, mainly in memory.c)
+ *        ->i_pages lock	(arch-dependent flush_dcache_mmap_lock)
+ *
+ *  ->mmap_lock
+ *    ->invalidate_lock		(filemap_fault)
+ *      ->lock_page		(filemap_fault, access_process_vm)
+ *
+ *  ->i_rwsem			(generic_perform_write)
+ *    ->mmap_lock		(fault_in_readable->do_page_fault)
+ *
+ *  bdi->wb.list_lock
+ *    sb_lock			(fs/fs-writeback.c)
+ *    ->i_pages lock		(__sync_single_inode)
+ *
+ *  ->i_mmap_rwsem
+ *    ->anon_vma.lock		(vma_merge)
+ *
+ *  ->anon_vma.lock
+ *    ->page_table_lock or pte_lock	(anon_vma_prepare and various)
+ *
+ *  ->page_table_lock or pte_lock
+ *    ->swap_lock		(try_to_unmap_one)
+ *    ->private_lock		(try_to_unmap_one)
+ *    ->i_pages lock		(try_to_unmap_one)
+ *    ->lruvec->lru_lock	(follow_page->mark_page_accessed)
+ *    ->lruvec->lru_lock	(check_pte_range->isolate_lru_page)
+ *    ->private_lock		(page_remove_rmap->set_page_dirty)
+ *    ->i_pages lock		(page_remove_rmap->set_page_dirty)
+ *    bdi.wb->list_lock		(page_remove_rmap->set_page_dirty)
+ *    ->inode->i_lock		(page_remove_rmap->set_page_dirty)
+ *    ->memcg->move_lock	(page_remove_rmap->folio_memcg_lock)
+ *    bdi.wb->list_lock		(zap_pte_range->set_page_dirty)
+ *    ->inode->i_lock		(zap_pte_range->set_page_dirty)
+ *    ->private_lock		(zap_pte_range->block_dirty_folio)
+ */
+
+static void page_cache_delete(struct address_space *mapping,
+				   struct folio *folio, void *shadow)
+{
+	XA_STATE(xas, &mapping->i_pages, folio->index);
+	long nr = 1;
+
+	mapping_set_update(&xas, mapping);
+
+	/* hugetlb pages are represented by a single entry in the xarray */
+	if (!folio_test_hugetlb(folio)) {
+		xas_set_order(&xas, folio->index, folio_order(folio));
+		nr = folio_nr_pages(folio);
+	}
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	xas_store(&xas, shadow);
+	xas_init_marks(&xas);
+
+	folio->mapping = NULL;
+	/* Leave page->index set: truncation lookup relies upon it */
+	mapping->nrpages -= nr;
+}
+
+static void filemap_unaccount_folio(struct address_space *mapping,
+		struct folio *folio)
+{
+	long nr;
+
+	VM_BUG_ON_FOLIO(folio_mapped(folio), folio);
+	if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(folio_mapped(folio))) {
+		pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
+			 current->comm, folio_pfn(folio));
+		dump_page(&folio->page, "still mapped when deleted");
+		dump_stack();
+		add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+
+		if (mapping_exiting(mapping) && !folio_test_large(folio)) {
+			int mapcount = page_mapcount(&folio->page);
+
+			if (folio_ref_count(folio) >= mapcount + 2) {
+				/*
+				 * All vmas have already been torn down, so it's
+				 * a good bet that actually the page is unmapped
+				 * and we'd rather not leak it: if we're wrong,
+				 * another bad page check should catch it later.
+				 */
+				page_mapcount_reset(&folio->page);
+				folio_ref_sub(folio, mapcount);
+			}
+		}
+	}
+
+	/* hugetlb folios do not participate in page cache accounting. */
+	if (folio_test_hugetlb(folio))
+		return;
+
+	nr = folio_nr_pages(folio);
+
+	__lruvec_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
+	if (folio_test_swapbacked(folio)) {
+		__lruvec_stat_mod_folio(folio, NR_SHMEM, -nr);
+		if (folio_test_pmd_mappable(folio))
+			__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr);
+	} else if (folio_test_pmd_mappable(folio)) {
+		__lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
+		filemap_nr_thps_dec(mapping);
+	}
+
+	/*
+	 * At this point folio must be either written or cleaned by
+	 * truncate.  Dirty folio here signals a bug and loss of
+	 * unwritten data - on ordinary filesystems.
+	 *
+	 * But it's harmless on in-memory filesystems like tmpfs; and can
+	 * occur when a driver which did get_user_pages() sets page dirty
+	 * before putting it, while the inode is being finally evicted.
+	 *
+	 * Below fixes dirty accounting after removing the folio entirely
+	 * but leaves the dirty flag set: it has no effect for truncated
+	 * folio and anyway will be cleared before returning folio to
+	 * buddy allocator.
+	 */
+	if (WARN_ON_ONCE(folio_test_dirty(folio) &&
+			 mapping_can_writeback(mapping)))
+		folio_account_cleaned(folio, inode_to_wb(mapping->host));
+}
+
+/*
+ * Delete a page from the page cache and free it. Caller has to make
+ * sure the page is locked and that nobody else uses it - or that usage
+ * is safe.  The caller must hold the i_pages lock.
+ */
+void __filemap_remove_folio(struct folio *folio, void *shadow)
+{
+	struct address_space *mapping = folio->mapping;
+
+	trace_mm_filemap_delete_from_page_cache(folio);
+	filemap_unaccount_folio(mapping, folio);
+	page_cache_delete(mapping, folio, shadow);
+}
+
+void filemap_free_folio(struct address_space *mapping, struct folio *folio)
+{
+	void (*free_folio)(struct folio *);
+	int refs = 1;
+
+	free_folio = mapping->a_ops->free_folio;
+	if (free_folio)
+		free_folio(folio);
+
+	if (folio_test_large(folio) && !folio_test_hugetlb(folio))
+		refs = folio_nr_pages(folio);
+	folio_put_refs(folio, refs);
+}
+
+/**
+ * filemap_remove_folio - Remove folio from page cache.
+ * @folio: The folio.
+ *
+ * This must be called only on folios that are locked and have been
+ * verified to be in the page cache.  It will never put the folio into
+ * the free list because the caller has a reference on the page.
+ */
+void filemap_remove_folio(struct folio *folio)
+{
+	struct address_space *mapping = folio->mapping;
+
+	BUG_ON(!folio_test_locked(folio));
+	spin_lock(&mapping->host->i_lock);
+	xa_lock_irq(&mapping->i_pages);
+	__filemap_remove_folio(folio, NULL);
+	xa_unlock_irq(&mapping->i_pages);
+	if (mapping_shrinkable(mapping))
+		inode_add_lru(mapping->host);
+	spin_unlock(&mapping->host->i_lock);
+
+	filemap_free_folio(mapping, folio);
+}
+
+/*
+ * page_cache_delete_batch - delete several folios from page cache
+ * @mapping: the mapping to which folios belong
+ * @fbatch: batch of folios to delete
+ *
+ * The function walks over mapping->i_pages and removes folios passed in
+ * @fbatch from the mapping. The function expects @fbatch to be sorted
+ * by page index and is optimised for it to be dense.
+ * It tolerates holes in @fbatch (mapping entries at those indices are not
+ * modified).
+ *
+ * The function expects the i_pages lock to be held.
+ */
+static void page_cache_delete_batch(struct address_space *mapping,
+			     struct folio_batch *fbatch)
+{
+	XA_STATE(xas, &mapping->i_pages, fbatch->folios[0]->index);
+	long total_pages = 0;
+	int i = 0;
+	struct folio *folio;
+
+	mapping_set_update(&xas, mapping);
+	xas_for_each(&xas, folio, ULONG_MAX) {
+		if (i >= folio_batch_count(fbatch))
+			break;
+
+		/* A swap/dax/shadow entry got inserted? Skip it. */
+		if (xa_is_value(folio))
+			continue;
+		/*
+		 * A page got inserted in our range? Skip it. We have our
+		 * pages locked so they are protected from being removed.
+		 * If we see a page whose index is higher than ours, it
+		 * means our page has been removed, which shouldn't be
+		 * possible because we're holding the PageLock.
+		 */
+		if (folio != fbatch->folios[i]) {
+			VM_BUG_ON_FOLIO(folio->index >
+					fbatch->folios[i]->index, folio);
+			continue;
+		}
+
+		WARN_ON_ONCE(!folio_test_locked(folio));
+
+		folio->mapping = NULL;
+		/* Leave folio->index set: truncation lookup relies on it */
+
+		i++;
+		xas_store(&xas, NULL);
+		total_pages += folio_nr_pages(folio);
+	}
+	mapping->nrpages -= total_pages;
+}
+
+void delete_from_page_cache_batch(struct address_space *mapping,
+				  struct folio_batch *fbatch)
+{
+	int i;
+
+	if (!folio_batch_count(fbatch))
+		return;
+
+	spin_lock(&mapping->host->i_lock);
+	xa_lock_irq(&mapping->i_pages);
+	for (i = 0; i < folio_batch_count(fbatch); i++) {
+		struct folio *folio = fbatch->folios[i];
+
+		trace_mm_filemap_delete_from_page_cache(folio);
+		filemap_unaccount_folio(mapping, folio);
+	}
+	page_cache_delete_batch(mapping, fbatch);
+	xa_unlock_irq(&mapping->i_pages);
+	if (mapping_shrinkable(mapping))
+		inode_add_lru(mapping->host);
+	spin_unlock(&mapping->host->i_lock);
+
+	for (i = 0; i < folio_batch_count(fbatch); i++)
+		filemap_free_folio(mapping, fbatch->folios[i]);
+}
+
+int filemap_check_errors(struct address_space *mapping)
+{
+	int ret = 0;
+	/* Check for outstanding write errors */
+	if (test_bit(AS_ENOSPC, &mapping->flags) &&
+	    test_and_clear_bit(AS_ENOSPC, &mapping->flags))
+		ret = -ENOSPC;
+	if (test_bit(AS_EIO, &mapping->flags) &&
+	    test_and_clear_bit(AS_EIO, &mapping->flags))
+		ret = -EIO;
+	return ret;
+}
+EXPORT_SYMBOL(filemap_check_errors);
+
+static int filemap_check_and_keep_errors(struct address_space *mapping)
+{
+	/* Check for outstanding write errors */
+	if (test_bit(AS_EIO, &mapping->flags))
+		return -EIO;
+	if (test_bit(AS_ENOSPC, &mapping->flags))
+		return -ENOSPC;
+	return 0;
+}
+
+/**
+ * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range
+ * @mapping:	address space structure to write
+ * @wbc:	the writeback_control controlling the writeout
+ *
+ * Call writepages on the mapping using the provided wbc to control the
+ * writeout.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int filemap_fdatawrite_wbc(struct address_space *mapping,
+			   struct writeback_control *wbc)
+{
+	int ret;
+
+	if (!mapping_can_writeback(mapping) ||
+	    !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
+		return 0;
+
+	wbc_attach_fdatawrite_inode(wbc, mapping->host);
+	ret = do_writepages(mapping, wbc);
+	wbc_detach_inode(wbc);
+	return ret;
+}
+EXPORT_SYMBOL(filemap_fdatawrite_wbc);
+
+/**
+ * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
+ * @mapping:	address space structure to write
+ * @start:	offset in bytes where the range starts
+ * @end:	offset in bytes where the range ends (inclusive)
+ * @sync_mode:	enable synchronous operation
+ *
+ * Start writeback against all of a mapping's dirty pages that lie
+ * within the byte offsets <start, end> inclusive.
+ *
+ * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
+ * opposed to a regular memory cleansing writeback.  The difference between
+ * these two operations is that if a dirty page/buffer is encountered, it must
+ * be waited upon, and not just skipped over.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
+				loff_t end, int sync_mode)
+{
+	struct writeback_control wbc = {
+		.sync_mode = sync_mode,
+		.nr_to_write = LONG_MAX,
+		.range_start = start,
+		.range_end = end,
+	};
+
+	return filemap_fdatawrite_wbc(mapping, &wbc);
+}
+
+static inline int __filemap_fdatawrite(struct address_space *mapping,
+	int sync_mode)
+{
+	return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
+}
+
+int filemap_fdatawrite(struct address_space *mapping)
+{
+	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
+}
+EXPORT_SYMBOL(filemap_fdatawrite);
+
+int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
+				loff_t end)
+{
+	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
+}
+EXPORT_SYMBOL(filemap_fdatawrite_range);
+
+/**
+ * filemap_flush - mostly a non-blocking flush
+ * @mapping:	target address_space
+ *
+ * This is a mostly non-blocking flush.  Not suitable for data-integrity
+ * purposes - I/O may not be started against all dirty pages.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int filemap_flush(struct address_space *mapping)
+{
+	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
+}
+EXPORT_SYMBOL(filemap_flush);
+
+/**
+ * filemap_range_has_page - check if a page exists in range.
+ * @mapping:           address space within which to check
+ * @start_byte:        offset in bytes where the range starts
+ * @end_byte:          offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback.
+ *
+ * Return: %true if at least one page exists in the specified range,
+ * %false otherwise.
+ */
+bool filemap_range_has_page(struct address_space *mapping,
+			   loff_t start_byte, loff_t end_byte)
+{
+	struct folio *folio;
+	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+	pgoff_t max = end_byte >> PAGE_SHIFT;
+
+	if (end_byte < start_byte)
+		return false;
+
+	rcu_read_lock();
+	for (;;) {
+		folio = xas_find(&xas, max);
+		if (xas_retry(&xas, folio))
+			continue;
+		/* Shadow entries don't count */
+		if (xa_is_value(folio))
+			continue;
+		/*
+		 * We don't need to try to pin this page; we're about to
+		 * release the RCU lock anyway.  It is enough to know that
+		 * there was a page here recently.
+		 */
+		break;
+	}
+	rcu_read_unlock();
+
+	return folio != NULL;
+}
+EXPORT_SYMBOL(filemap_range_has_page);
+
+static void __filemap_fdatawait_range(struct address_space *mapping,
+				     loff_t start_byte, loff_t end_byte)
+{
+	pgoff_t index = start_byte >> PAGE_SHIFT;
+	pgoff_t end = end_byte >> PAGE_SHIFT;
+	struct folio_batch fbatch;
+	unsigned nr_folios;
+
+	folio_batch_init(&fbatch);
+
+	while (index <= end) {
+		unsigned i;
+
+		nr_folios = filemap_get_folios_tag(mapping, &index, end,
+				PAGECACHE_TAG_WRITEBACK, &fbatch);
+
+		if (!nr_folios)
+			break;
+
+		for (i = 0; i < nr_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			folio_wait_writeback(folio);
+			folio_clear_error(folio);
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+}
+
+/**
+ * filemap_fdatawait_range - wait for writeback to complete
+ * @mapping:		address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the given address space
+ * in the given range and wait for all of them.  Check error status of
+ * the address space and return it.
+ *
+ * Since the error status of the address space is cleared by this function,
+ * callers are responsible for checking the return value and handling and/or
+ * reporting the error.
+ *
+ * Return: error status of the address space.
+ */
+int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
+			    loff_t end_byte)
+{
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return filemap_check_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_fdatawait_range);
+
+/**
+ * filemap_fdatawait_range_keep_errors - wait for writeback to complete
+ * @mapping:		address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the given address space in the
+ * given range and wait for all of them.  Unlike filemap_fdatawait_range(),
+ * this function does not clear error status of the address space.
+ *
+ * Use this function if callers don't handle errors themselves.  Expected
+ * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
+ * fsfreeze(8)
+ */
+int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
+		loff_t start_byte, loff_t end_byte)
+{
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return filemap_check_and_keep_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_fdatawait_range_keep_errors);
+
+/**
+ * file_fdatawait_range - wait for writeback to complete
+ * @file:		file pointing to address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the address space that file
+ * refers to, in the given range and wait for all of them.  Check error
+ * status of the address space vs. the file->f_wb_err cursor and return it.
+ *
+ * Since the error status of the file is advanced by this function,
+ * callers are responsible for checking the return value and handling and/or
+ * reporting the error.
+ *
+ * Return: error status of the address space vs. the file->f_wb_err cursor.
+ */
+int file_fdatawait_range(struct file *file, loff_t start_byte, loff_t end_byte)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return file_check_and_advance_wb_err(file);
+}
+EXPORT_SYMBOL(file_fdatawait_range);
+
+/**
+ * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
+ * @mapping: address space structure to wait for
+ *
+ * Walk the list of under-writeback pages of the given address space
+ * and wait for all of them.  Unlike filemap_fdatawait(), this function
+ * does not clear error status of the address space.
+ *
+ * Use this function if callers don't handle errors themselves.  Expected
+ * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
+ * fsfreeze(8)
+ *
+ * Return: error status of the address space.
+ */
+int filemap_fdatawait_keep_errors(struct address_space *mapping)
+{
+	__filemap_fdatawait_range(mapping, 0, LLONG_MAX);
+	return filemap_check_and_keep_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
+
+/* Returns true if writeback might be needed or already in progress. */
+static bool mapping_needs_writeback(struct address_space *mapping)
+{
+	return mapping->nrpages;
+}
+
+bool filemap_range_has_writeback(struct address_space *mapping,
+				 loff_t start_byte, loff_t end_byte)
+{
+	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+	pgoff_t max = end_byte >> PAGE_SHIFT;
+	struct folio *folio;
+
+	if (end_byte < start_byte)
+		return false;
+
+	rcu_read_lock();
+	xas_for_each(&xas, folio, max) {
+		if (xas_retry(&xas, folio))
+			continue;
+		if (xa_is_value(folio))
+			continue;
+		if (folio_test_dirty(folio) || folio_test_locked(folio) ||
+				folio_test_writeback(folio))
+			break;
+	}
+	rcu_read_unlock();
+	return folio != NULL;
+}
+EXPORT_SYMBOL_GPL(filemap_range_has_writeback);
+
+/**
+ * filemap_write_and_wait_range - write out & wait on a file range
+ * @mapping:	the address_space for the pages
+ * @lstart:	offset in bytes where the range starts
+ * @lend:	offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that @lend is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ *
+ * Return: error status of the address space.
+ */
+int filemap_write_and_wait_range(struct address_space *mapping,
+				 loff_t lstart, loff_t lend)
+{
+	int err = 0, err2;
+
+	if (lend < lstart)
+		return 0;
+
+	if (mapping_needs_writeback(mapping)) {
+		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+						 WB_SYNC_ALL);
+		/*
+		 * Even if the above returned error, the pages may be
+		 * written partially (e.g. -ENOSPC), so we wait for it.
+		 * But the -EIO is special case, it may indicate the worst
+		 * thing (e.g. bug) happened, so we avoid waiting for it.
+		 */
+		if (err != -EIO)
+			__filemap_fdatawait_range(mapping, lstart, lend);
+	}
+	err2 = filemap_check_errors(mapping);
+	if (!err)
+		err = err2;
+	return err;
+}
+EXPORT_SYMBOL(filemap_write_and_wait_range);
+
+void __filemap_set_wb_err(struct address_space *mapping, int err)
+{
+	errseq_t eseq = errseq_set(&mapping->wb_err, err);
+
+	trace_filemap_set_wb_err(mapping, eseq);
+}
+EXPORT_SYMBOL(__filemap_set_wb_err);
+
+/**
+ * file_check_and_advance_wb_err - report wb error (if any) that was previously
+ * 				   and advance wb_err to current one
+ * @file: struct file on which the error is being reported
+ *
+ * When userland calls fsync (or something like nfsd does the equivalent), we
+ * want to report any writeback errors that occurred since the last fsync (or
+ * since the file was opened if there haven't been any).
+ *
+ * Grab the wb_err from the mapping. If it matches what we have in the file,
+ * then just quickly return 0. The file is all caught up.
+ *
+ * If it doesn't match, then take the mapping value, set the "seen" flag in
+ * it and try to swap it into place. If it works, or another task beat us
+ * to it with the new value, then update the f_wb_err and return the error
+ * portion. The error at this point must be reported via proper channels
+ * (a'la fsync, or NFS COMMIT operation, etc.).
+ *
+ * While we handle mapping->wb_err with atomic operations, the f_wb_err
+ * value is protected by the f_lock since we must ensure that it reflects
+ * the latest value swapped in for this file descriptor.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int file_check_and_advance_wb_err(struct file *file)
+{
+	int err = 0;
+	errseq_t old = READ_ONCE(file->f_wb_err);
+	struct address_space *mapping = file->f_mapping;
+
+	/* Locklessly handle the common case where nothing has changed */
+	if (errseq_check(&mapping->wb_err, old)) {
+		/* Something changed, must use slow path */
+		spin_lock(&file->f_lock);
+		old = file->f_wb_err;
+		err = errseq_check_and_advance(&mapping->wb_err,
+						&file->f_wb_err);
+		trace_file_check_and_advance_wb_err(file, old);
+		spin_unlock(&file->f_lock);
+	}
+
+	/*
+	 * We're mostly using this function as a drop in replacement for
+	 * filemap_check_errors. Clear AS_EIO/AS_ENOSPC to emulate the effect
+	 * that the legacy code would have had on these flags.
+	 */
+	clear_bit(AS_EIO, &mapping->flags);
+	clear_bit(AS_ENOSPC, &mapping->flags);
+	return err;
+}
+EXPORT_SYMBOL(file_check_and_advance_wb_err);
+
+/**
+ * file_write_and_wait_range - write out & wait on a file range
+ * @file:	file pointing to address_space with pages
+ * @lstart:	offset in bytes where the range starts
+ * @lend:	offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that @lend is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ *
+ * After writing out and waiting on the data, we check and advance the
+ * f_wb_err cursor to the latest value, and return any errors detected there.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
+{
+	int err = 0, err2;
+	struct address_space *mapping = file->f_mapping;
+
+	if (lend < lstart)
+		return 0;
+
+	if (mapping_needs_writeback(mapping)) {
+		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+						 WB_SYNC_ALL);
+		/* See comment of filemap_write_and_wait() */
+		if (err != -EIO)
+			__filemap_fdatawait_range(mapping, lstart, lend);
+	}
+	err2 = file_check_and_advance_wb_err(file);
+	if (!err)
+		err = err2;
+	return err;
+}
+EXPORT_SYMBOL(file_write_and_wait_range);
+
+/**
+ * replace_page_cache_folio - replace a pagecache folio with a new one
+ * @old:	folio to be replaced
+ * @new:	folio to replace with
+ *
+ * This function replaces a folio in the pagecache with a new one.  On
+ * success it acquires the pagecache reference for the new folio and
+ * drops it for the old folio.  Both the old and new folios must be
+ * locked.  This function does not add the new folio to the LRU, the
+ * caller must do that.
+ *
+ * The remove + add is atomic.  This function cannot fail.
+ */
+void replace_page_cache_folio(struct folio *old, struct folio *new)
+{
+	struct address_space *mapping = old->mapping;
+	void (*free_folio)(struct folio *) = mapping->a_ops->free_folio;
+	pgoff_t offset = old->index;
+	XA_STATE(xas, &mapping->i_pages, offset);
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(old), old);
+	VM_BUG_ON_FOLIO(!folio_test_locked(new), new);
+	VM_BUG_ON_FOLIO(new->mapping, new);
+
+	folio_get(new);
+	new->mapping = mapping;
+	new->index = offset;
+
+	mem_cgroup_migrate(old, new);
+
+	xas_lock_irq(&xas);
+	xas_store(&xas, new);
+
+	old->mapping = NULL;
+	/* hugetlb pages do not participate in page cache accounting. */
+	if (!folio_test_hugetlb(old))
+		__lruvec_stat_sub_folio(old, NR_FILE_PAGES);
+	if (!folio_test_hugetlb(new))
+		__lruvec_stat_add_folio(new, NR_FILE_PAGES);
+	if (folio_test_swapbacked(old))
+		__lruvec_stat_sub_folio(old, NR_SHMEM);
+	if (folio_test_swapbacked(new))
+		__lruvec_stat_add_folio(new, NR_SHMEM);
+	xas_unlock_irq(&xas);
+	if (free_folio)
+		free_folio(old);
+	folio_put(old);
+}
+EXPORT_SYMBOL_GPL(replace_page_cache_folio);
+
+noinline int __filemap_add_folio(struct address_space *mapping,
+		struct folio *folio, pgoff_t index, gfp_t gfp, void **shadowp)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	int huge = folio_test_hugetlb(folio);
+	bool charged = false;
+	long nr = 1;
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
+	mapping_set_update(&xas, mapping);
+
+	if (!huge) {
+		int error = mem_cgroup_charge(folio, NULL, gfp);
+		VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
+		if (error)
+			return error;
+		charged = true;
+		xas_set_order(&xas, index, folio_order(folio));
+		nr = folio_nr_pages(folio);
+	}
+
+	gfp &= GFP_RECLAIM_MASK;
+	folio_ref_add(folio, nr);
+	folio->mapping = mapping;
+	folio->index = xas.xa_index;
+
+	do {
+		unsigned int order = xa_get_order(xas.xa, xas.xa_index);
+		void *entry, *old = NULL;
+
+		if (order > folio_order(folio))
+			xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index),
+					order, gfp);
+		xas_lock_irq(&xas);
+		xas_for_each_conflict(&xas, entry) {
+			old = entry;
+			if (!xa_is_value(entry)) {
+				xas_set_err(&xas, -EEXIST);
+				goto unlock;
+			}
+		}
+
+		if (old) {
+			if (shadowp)
+				*shadowp = old;
+			/* entry may have been split before we acquired lock */
+			order = xa_get_order(xas.xa, xas.xa_index);
+			if (order > folio_order(folio)) {
+				/* How to handle large swap entries? */
+				BUG_ON(shmem_mapping(mapping));
+				xas_split(&xas, old, order);
+				xas_reset(&xas);
+			}
+		}
+
+		xas_store(&xas, folio);
+		if (xas_error(&xas))
+			goto unlock;
+
+		mapping->nrpages += nr;
+
+		/* hugetlb pages do not participate in page cache accounting */
+		if (!huge) {
+			__lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr);
+			if (folio_test_pmd_mappable(folio))
+				__lruvec_stat_mod_folio(folio,
+						NR_FILE_THPS, nr);
+		}
+unlock:
+		xas_unlock_irq(&xas);
+	} while (xas_nomem(&xas, gfp));
+
+	if (xas_error(&xas))
+		goto error;
+
+	trace_mm_filemap_add_to_page_cache(folio);
+	return 0;
+error:
+	if (charged)
+		mem_cgroup_uncharge(folio);
+	folio->mapping = NULL;
+	/* Leave page->index set: truncation relies upon it */
+	folio_put_refs(folio, nr);
+	return xas_error(&xas);
+}
+ALLOW_ERROR_INJECTION(__filemap_add_folio, ERRNO);
+
+int filemap_add_folio(struct address_space *mapping, struct folio *folio,
+				pgoff_t index, gfp_t gfp)
+{
+	void *shadow = NULL;
+	int ret;
+
+	__folio_set_locked(folio);
+	ret = __filemap_add_folio(mapping, folio, index, gfp, &shadow);
+	if (unlikely(ret))
+		__folio_clear_locked(folio);
+	else {
+		/*
+		 * The folio might have been evicted from cache only
+		 * recently, in which case it should be activated like
+		 * any other repeatedly accessed folio.
+		 * The exception is folios getting rewritten; evicting other
+		 * data from the working set, only to cache data that will
+		 * get overwritten with something else, is a waste of memory.
+		 */
+		WARN_ON_ONCE(folio_test_active(folio));
+		if (!(gfp & __GFP_WRITE) && shadow)
+			workingset_refault(folio, shadow);
+		folio_add_lru(folio);
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(filemap_add_folio);
+
+#ifdef CONFIG_NUMA
+struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order)
+{
+	int n;
+	struct folio *folio;
+
+	if (cpuset_do_page_mem_spread()) {
+		unsigned int cpuset_mems_cookie;
+		do {
+			cpuset_mems_cookie = read_mems_allowed_begin();
+			n = cpuset_mem_spread_node();
+			folio = __folio_alloc_node(gfp, order, n);
+		} while (!folio && read_mems_allowed_retry(cpuset_mems_cookie));
+
+		return folio;
+	}
+	return folio_alloc(gfp, order);
+}
+EXPORT_SYMBOL(filemap_alloc_folio);
+#endif
+
+/*
+ * filemap_invalidate_lock_two - lock invalidate_lock for two mappings
+ *
+ * Lock exclusively invalidate_lock of any passed mapping that is not NULL.
+ *
+ * @mapping1: the first mapping to lock
+ * @mapping2: the second mapping to lock
+ */
+void filemap_invalidate_lock_two(struct address_space *mapping1,
+				 struct address_space *mapping2)
+{
+	if (mapping1 > mapping2)
+		swap(mapping1, mapping2);
+	if (mapping1)
+		down_write(&mapping1->invalidate_lock);
+	if (mapping2 && mapping1 != mapping2)
+		down_write_nested(&mapping2->invalidate_lock, 1);
+}
+EXPORT_SYMBOL(filemap_invalidate_lock_two);
+
+/*
+ * filemap_invalidate_unlock_two - unlock invalidate_lock for two mappings
+ *
+ * Unlock exclusive invalidate_lock of any passed mapping that is not NULL.
+ *
+ * @mapping1: the first mapping to unlock
+ * @mapping2: the second mapping to unlock
+ */
+void filemap_invalidate_unlock_two(struct address_space *mapping1,
+				   struct address_space *mapping2)
+{
+	if (mapping1)
+		up_write(&mapping1->invalidate_lock);
+	if (mapping2 && mapping1 != mapping2)
+		up_write(&mapping2->invalidate_lock);
+}
+EXPORT_SYMBOL(filemap_invalidate_unlock_two);
+
+/*
+ * In order to wait for pages to become available there must be
+ * waitqueues associated with pages. By using a hash table of
+ * waitqueues where the bucket discipline is to maintain all
+ * waiters on the same queue and wake all when any of the pages
+ * become available, and for the woken contexts to check to be
+ * sure the appropriate page became available, this saves space
+ * at a cost of "thundering herd" phenomena during rare hash
+ * collisions.
+ */
+#define PAGE_WAIT_TABLE_BITS 8
+#define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
+static wait_queue_head_t folio_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
+
+static wait_queue_head_t *folio_waitqueue(struct folio *folio)
+{
+	return &folio_wait_table[hash_ptr(folio, PAGE_WAIT_TABLE_BITS)];
+}
+
+void __init pagecache_init(void)
+{
+	int i;
+
+	for (i = 0; i < PAGE_WAIT_TABLE_SIZE; i++)
+		init_waitqueue_head(&folio_wait_table[i]);
+
+	page_writeback_init();
+}
+
+/*
+ * The page wait code treats the "wait->flags" somewhat unusually, because
+ * we have multiple different kinds of waits, not just the usual "exclusive"
+ * one.
+ *
+ * We have:
+ *
+ *  (a) no special bits set:
+ *
+ *	We're just waiting for the bit to be released, and when a waker
+ *	calls the wakeup function, we set WQ_FLAG_WOKEN and wake it up,
+ *	and remove it from the wait queue.
+ *
+ *	Simple and straightforward.
+ *
+ *  (b) WQ_FLAG_EXCLUSIVE:
+ *
+ *	The waiter is waiting to get the lock, and only one waiter should
+ *	be woken up to avoid any thundering herd behavior. We'll set the
+ *	WQ_FLAG_WOKEN bit, wake it up, and remove it from the wait queue.
+ *
+ *	This is the traditional exclusive wait.
+ *
+ *  (c) WQ_FLAG_EXCLUSIVE | WQ_FLAG_CUSTOM:
+ *
+ *	The waiter is waiting to get the bit, and additionally wants the
+ *	lock to be transferred to it for fair lock behavior. If the lock
+ *	cannot be taken, we stop walking the wait queue without waking
+ *	the waiter.
+ *
+ *	This is the "fair lock handoff" case, and in addition to setting
+ *	WQ_FLAG_WOKEN, we set WQ_FLAG_DONE to let the waiter easily see
+ *	that it now has the lock.
+ */
+static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
+{
+	unsigned int flags;
+	struct wait_page_key *key = arg;
+	struct wait_page_queue *wait_page
+		= container_of(wait, struct wait_page_queue, wait);
+
+	if (!wake_page_match(wait_page, key))
+		return 0;
+
+	/*
+	 * If it's a lock handoff wait, we get the bit for it, and
+	 * stop walking (and do not wake it up) if we can't.
+	 */
+	flags = wait->flags;
+	if (flags & WQ_FLAG_EXCLUSIVE) {
+		if (test_bit(key->bit_nr, &key->folio->flags))
+			return -1;
+		if (flags & WQ_FLAG_CUSTOM) {
+			if (test_and_set_bit(key->bit_nr, &key->folio->flags))
+				return -1;
+			flags |= WQ_FLAG_DONE;
+		}
+	}
+
+	/*
+	 * We are holding the wait-queue lock, but the waiter that
+	 * is waiting for this will be checking the flags without
+	 * any locking.
+	 *
+	 * So update the flags atomically, and wake up the waiter
+	 * afterwards to avoid any races. This store-release pairs
+	 * with the load-acquire in folio_wait_bit_common().
+	 */
+	smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
+	wake_up_state(wait->private, mode);
+
+	/*
+	 * Ok, we have successfully done what we're waiting for,
+	 * and we can unconditionally remove the wait entry.
+	 *
+	 * Note that this pairs with the "finish_wait()" in the
+	 * waiter, and has to be the absolute last thing we do.
+	 * After this list_del_init(&wait->entry) the wait entry
+	 * might be de-allocated and the process might even have
+	 * exited.
+	 */
+	list_del_init_careful(&wait->entry);
+	return (flags & WQ_FLAG_EXCLUSIVE) != 0;
+}
+
+static void folio_wake_bit(struct folio *folio, int bit_nr)
+{
+	wait_queue_head_t *q = folio_waitqueue(folio);
+	struct wait_page_key key;
+	unsigned long flags;
+	wait_queue_entry_t bookmark;
+
+	key.folio = folio;
+	key.bit_nr = bit_nr;
+	key.page_match = 0;
+
+	bookmark.flags = 0;
+	bookmark.private = NULL;
+	bookmark.func = NULL;
+	INIT_LIST_HEAD(&bookmark.entry);
+
+	spin_lock_irqsave(&q->lock, flags);
+	__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
+
+	while (bookmark.flags & WQ_FLAG_BOOKMARK) {
+		/*
+		 * Take a breather from holding the lock,
+		 * allow pages that finish wake up asynchronously
+		 * to acquire the lock and remove themselves
+		 * from wait queue
+		 */
+		spin_unlock_irqrestore(&q->lock, flags);
+		cpu_relax();
+		spin_lock_irqsave(&q->lock, flags);
+		__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
+	}
+
+	/*
+	 * It's possible to miss clearing waiters here, when we woke our page
+	 * waiters, but the hashed waitqueue has waiters for other pages on it.
+	 * That's okay, it's a rare case. The next waker will clear it.
+	 *
+	 * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE,
+	 * other), the flag may be cleared in the course of freeing the page;
+	 * but that is not required for correctness.
+	 */
+	if (!waitqueue_active(q) || !key.page_match)
+		folio_clear_waiters(folio);
+
+	spin_unlock_irqrestore(&q->lock, flags);
+}
+
+static void folio_wake(struct folio *folio, int bit)
+{
+	if (!folio_test_waiters(folio))
+		return;
+	folio_wake_bit(folio, bit);
+}
+
+/*
+ * A choice of three behaviors for folio_wait_bit_common():
+ */
+enum behavior {
+	EXCLUSIVE,	/* Hold ref to page and take the bit when woken, like
+			 * __folio_lock() waiting on then setting PG_locked.
+			 */
+	SHARED,		/* Hold ref to page and check the bit when woken, like
+			 * folio_wait_writeback() waiting on PG_writeback.
+			 */
+	DROP,		/* Drop ref to page before wait, no check when woken,
+			 * like folio_put_wait_locked() on PG_locked.
+			 */
+};
+
+/*
+ * Attempt to check (or get) the folio flag, and mark us done
+ * if successful.
+ */
+static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
+					struct wait_queue_entry *wait)
+{
+	if (wait->flags & WQ_FLAG_EXCLUSIVE) {
+		if (test_and_set_bit(bit_nr, &folio->flags))
+			return false;
+	} else if (test_bit(bit_nr, &folio->flags))
+		return false;
+
+	wait->flags |= WQ_FLAG_WOKEN | WQ_FLAG_DONE;
+	return true;
+}
+
+/* How many times do we accept lock stealing from under a waiter? */
+int sysctl_page_lock_unfairness = 5;
+
+static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
+		int state, enum behavior behavior)
+{
+	wait_queue_head_t *q = folio_waitqueue(folio);
+	int unfairness = sysctl_page_lock_unfairness;
+	struct wait_page_queue wait_page;
+	wait_queue_entry_t *wait = &wait_page.wait;
+	bool thrashing = false;
+	unsigned long pflags;
+	bool in_thrashing;
+
+	if (bit_nr == PG_locked &&
+	    !folio_test_uptodate(folio) && folio_test_workingset(folio)) {
+		delayacct_thrashing_start(&in_thrashing);
+		psi_memstall_enter(&pflags);
+		thrashing = true;
+	}
+
+	init_wait(wait);
+	wait->func = wake_page_function;
+	wait_page.folio = folio;
+	wait_page.bit_nr = bit_nr;
+
+repeat:
+	wait->flags = 0;
+	if (behavior == EXCLUSIVE) {
+		wait->flags = WQ_FLAG_EXCLUSIVE;
+		if (--unfairness < 0)
+			wait->flags |= WQ_FLAG_CUSTOM;
+	}
+
+	/*
+	 * Do one last check whether we can get the
+	 * page bit synchronously.
+	 *
+	 * Do the folio_set_waiters() marking before that
+	 * to let any waker we _just_ missed know they
+	 * need to wake us up (otherwise they'll never
+	 * even go to the slow case that looks at the
+	 * page queue), and add ourselves to the wait
+	 * queue if we need to sleep.
+	 *
+	 * This part needs to be done under the queue
+	 * lock to avoid races.
+	 */
+	spin_lock_irq(&q->lock);
+	folio_set_waiters(folio);
+	if (!folio_trylock_flag(folio, bit_nr, wait))
+		__add_wait_queue_entry_tail(q, wait);
+	spin_unlock_irq(&q->lock);
+
+	/*
+	 * From now on, all the logic will be based on
+	 * the WQ_FLAG_WOKEN and WQ_FLAG_DONE flag, to
+	 * see whether the page bit testing has already
+	 * been done by the wake function.
+	 *
+	 * We can drop our reference to the folio.
+	 */
+	if (behavior == DROP)
+		folio_put(folio);
+
+	/*
+	 * Note that until the "finish_wait()", or until
+	 * we see the WQ_FLAG_WOKEN flag, we need to
+	 * be very careful with the 'wait->flags', because
+	 * we may race with a waker that sets them.
+	 */
+	for (;;) {
+		unsigned int flags;
+
+		set_current_state(state);
+
+		/* Loop until we've been woken or interrupted */
+		flags = smp_load_acquire(&wait->flags);
+		if (!(flags & WQ_FLAG_WOKEN)) {
+			if (signal_pending_state(state, current))
+				break;
+
+			io_schedule();
+			continue;
+		}
+
+		/* If we were non-exclusive, we're done */
+		if (behavior != EXCLUSIVE)
+			break;
+
+		/* If the waker got the lock for us, we're done */
+		if (flags & WQ_FLAG_DONE)
+			break;
+
+		/*
+		 * Otherwise, if we're getting the lock, we need to
+		 * try to get it ourselves.
+		 *
+		 * And if that fails, we'll have to retry this all.
+		 */
+		if (unlikely(test_and_set_bit(bit_nr, folio_flags(folio, 0))))
+			goto repeat;
+
+		wait->flags |= WQ_FLAG_DONE;
+		break;
+	}
+
+	/*
+	 * If a signal happened, this 'finish_wait()' may remove the last
+	 * waiter from the wait-queues, but the folio waiters bit will remain
+	 * set. That's ok. The next wakeup will take care of it, and trying
+	 * to do it here would be difficult and prone to races.
+	 */
+	finish_wait(q, wait);
+
+	if (thrashing) {
+		delayacct_thrashing_end(&in_thrashing);
+		psi_memstall_leave(&pflags);
+	}
+
+	/*
+	 * NOTE! The wait->flags weren't stable until we've done the
+	 * 'finish_wait()', and we could have exited the loop above due
+	 * to a signal, and had a wakeup event happen after the signal
+	 * test but before the 'finish_wait()'.
+	 *
+	 * So only after the finish_wait() can we reliably determine
+	 * if we got woken up or not, so we can now figure out the final
+	 * return value based on that state without races.
+	 *
+	 * Also note that WQ_FLAG_WOKEN is sufficient for a non-exclusive
+	 * waiter, but an exclusive one requires WQ_FLAG_DONE.
+	 */
+	if (behavior == EXCLUSIVE)
+		return wait->flags & WQ_FLAG_DONE ? 0 : -EINTR;
+
+	return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
+}
+
+#ifdef CONFIG_MIGRATION
+/**
+ * migration_entry_wait_on_locked - Wait for a migration entry to be removed
+ * @entry: migration swap entry.
+ * @ptl: already locked ptl. This function will drop the lock.
+ *
+ * Wait for a migration entry referencing the given page to be removed. This is
+ * equivalent to put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE) except
+ * this can be called without taking a reference on the page. Instead this
+ * should be called while holding the ptl for the migration entry referencing
+ * the page.
+ *
+ * Returns after unlocking the ptl.
+ *
+ * This follows the same logic as folio_wait_bit_common() so see the comments
+ * there.
+ */
+void migration_entry_wait_on_locked(swp_entry_t entry, spinlock_t *ptl)
+	__releases(ptl)
+{
+	struct wait_page_queue wait_page;
+	wait_queue_entry_t *wait = &wait_page.wait;
+	bool thrashing = false;
+	unsigned long pflags;
+	bool in_thrashing;
+	wait_queue_head_t *q;
+	struct folio *folio = page_folio(pfn_swap_entry_to_page(entry));
+
+	q = folio_waitqueue(folio);
+	if (!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
+		delayacct_thrashing_start(&in_thrashing);
+		psi_memstall_enter(&pflags);
+		thrashing = true;
+	}
+
+	init_wait(wait);
+	wait->func = wake_page_function;
+	wait_page.folio = folio;
+	wait_page.bit_nr = PG_locked;
+	wait->flags = 0;
+
+	spin_lock_irq(&q->lock);
+	folio_set_waiters(folio);
+	if (!folio_trylock_flag(folio, PG_locked, wait))
+		__add_wait_queue_entry_tail(q, wait);
+	spin_unlock_irq(&q->lock);
+
+	/*
+	 * If a migration entry exists for the page the migration path must hold
+	 * a valid reference to the page, and it must take the ptl to remove the
+	 * migration entry. So the page is valid until the ptl is dropped.
+	 */
+	spin_unlock(ptl);
+
+	for (;;) {
+		unsigned int flags;
+
+		set_current_state(TASK_UNINTERRUPTIBLE);
+
+		/* Loop until we've been woken or interrupted */
+		flags = smp_load_acquire(&wait->flags);
+		if (!(flags & WQ_FLAG_WOKEN)) {
+			if (signal_pending_state(TASK_UNINTERRUPTIBLE, current))
+				break;
+
+			io_schedule();
+			continue;
+		}
+		break;
+	}
+
+	finish_wait(q, wait);
+
+	if (thrashing) {
+		delayacct_thrashing_end(&in_thrashing);
+		psi_memstall_leave(&pflags);
+	}
+}
+#endif
+
+void folio_wait_bit(struct folio *folio, int bit_nr)
+{
+	folio_wait_bit_common(folio, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
+}
+EXPORT_SYMBOL(folio_wait_bit);
+
+int folio_wait_bit_killable(struct folio *folio, int bit_nr)
+{
+	return folio_wait_bit_common(folio, bit_nr, TASK_KILLABLE, SHARED);
+}
+EXPORT_SYMBOL(folio_wait_bit_killable);
+
+/**
+ * folio_put_wait_locked - Drop a reference and wait for it to be unlocked
+ * @folio: The folio to wait for.
+ * @state: The sleep state (TASK_KILLABLE, TASK_UNINTERRUPTIBLE, etc).
+ *
+ * The caller should hold a reference on @folio.  They expect the page to
+ * become unlocked relatively soon, but do not wish to hold up migration
+ * (for example) by holding the reference while waiting for the folio to
+ * come unlocked.  After this function returns, the caller should not
+ * dereference @folio.
+ *
+ * Return: 0 if the folio was unlocked or -EINTR if interrupted by a signal.
+ */
+static int folio_put_wait_locked(struct folio *folio, int state)
+{
+	return folio_wait_bit_common(folio, PG_locked, state, DROP);
+}
+
+/**
+ * folio_add_wait_queue - Add an arbitrary waiter to a folio's wait queue
+ * @folio: Folio defining the wait queue of interest
+ * @waiter: Waiter to add to the queue
+ *
+ * Add an arbitrary @waiter to the wait queue for the nominated @folio.
+ */
+void folio_add_wait_queue(struct folio *folio, wait_queue_entry_t *waiter)
+{
+	wait_queue_head_t *q = folio_waitqueue(folio);
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->lock, flags);
+	__add_wait_queue_entry_tail(q, waiter);
+	folio_set_waiters(folio);
+	spin_unlock_irqrestore(&q->lock, flags);
+}
+EXPORT_SYMBOL_GPL(folio_add_wait_queue);
+
+#ifndef clear_bit_unlock_is_negative_byte
+
+/*
+ * PG_waiters is the high bit in the same byte as PG_lock.
+ *
+ * On x86 (and on many other architectures), we can clear PG_lock and
+ * test the sign bit at the same time. But if the architecture does
+ * not support that special operation, we just do this all by hand
+ * instead.
+ *
+ * The read of PG_waiters has to be after (or concurrently with) PG_locked
+ * being cleared, but a memory barrier should be unnecessary since it is
+ * in the same byte as PG_locked.
+ */
+static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem)
+{
+	clear_bit_unlock(nr, mem);
+	/* smp_mb__after_atomic(); */
+	return test_bit(PG_waiters, mem);
+}
+
+#endif
+
+/**
+ * folio_unlock - Unlock a locked folio.
+ * @folio: The folio.
+ *
+ * Unlocks the folio and wakes up any thread sleeping on the page lock.
+ *
+ * Context: May be called from interrupt or process context.  May not be
+ * called from NMI context.
+ */
+void folio_unlock(struct folio *folio)
+{
+	/* Bit 7 allows x86 to check the byte's sign bit */
+	BUILD_BUG_ON(PG_waiters != 7);
+	BUILD_BUG_ON(PG_locked > 7);
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	if (clear_bit_unlock_is_negative_byte(PG_locked, folio_flags(folio, 0)))
+		folio_wake_bit(folio, PG_locked);
+}
+EXPORT_SYMBOL(folio_unlock);
+
+/**
+ * folio_end_private_2 - Clear PG_private_2 and wake any waiters.
+ * @folio: The folio.
+ *
+ * Clear the PG_private_2 bit on a folio and wake up any sleepers waiting for
+ * it.  The folio reference held for PG_private_2 being set is released.
+ *
+ * This is, for example, used when a netfs folio is being written to a local
+ * disk cache, thereby allowing writes to the cache for the same folio to be
+ * serialised.
+ */
+void folio_end_private_2(struct folio *folio)
+{
+	VM_BUG_ON_FOLIO(!folio_test_private_2(folio), folio);
+	clear_bit_unlock(PG_private_2, folio_flags(folio, 0));
+	folio_wake_bit(folio, PG_private_2);
+	folio_put(folio);
+}
+EXPORT_SYMBOL(folio_end_private_2);
+
+/**
+ * folio_wait_private_2 - Wait for PG_private_2 to be cleared on a folio.
+ * @folio: The folio to wait on.
+ *
+ * Wait for PG_private_2 (aka PG_fscache) to be cleared on a folio.
+ */
+void folio_wait_private_2(struct folio *folio)
+{
+	while (folio_test_private_2(folio))
+		folio_wait_bit(folio, PG_private_2);
+}
+EXPORT_SYMBOL(folio_wait_private_2);
+
+/**
+ * folio_wait_private_2_killable - Wait for PG_private_2 to be cleared on a folio.
+ * @folio: The folio to wait on.
+ *
+ * Wait for PG_private_2 (aka PG_fscache) to be cleared on a folio or until a
+ * fatal signal is received by the calling task.
+ *
+ * Return:
+ * - 0 if successful.
+ * - -EINTR if a fatal signal was encountered.
+ */
+int folio_wait_private_2_killable(struct folio *folio)
+{
+	int ret = 0;
+
+	while (folio_test_private_2(folio)) {
+		ret = folio_wait_bit_killable(folio, PG_private_2);
+		if (ret < 0)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(folio_wait_private_2_killable);
+
+/**
+ * folio_end_writeback - End writeback against a folio.
+ * @folio: The folio.
+ */
+void folio_end_writeback(struct folio *folio)
+{
+	/*
+	 * folio_test_clear_reclaim() could be used here but it is an
+	 * atomic operation and overkill in this particular case. Failing
+	 * to shuffle a folio marked for immediate reclaim is too mild
+	 * a gain to justify taking an atomic operation penalty at the
+	 * end of every folio writeback.
+	 */
+	if (folio_test_reclaim(folio)) {
+		folio_clear_reclaim(folio);
+		folio_rotate_reclaimable(folio);
+	}
+
+	/*
+	 * Writeback does not hold a folio reference of its own, relying
+	 * on truncation to wait for the clearing of PG_writeback.
+	 * But here we must make sure that the folio is not freed and
+	 * reused before the folio_wake().
+	 */
+	folio_get(folio);
+	if (!__folio_end_writeback(folio))
+		BUG();
+
+	smp_mb__after_atomic();
+	folio_wake(folio, PG_writeback);
+	acct_reclaim_writeback(folio);
+	folio_put(folio);
+}
+EXPORT_SYMBOL(folio_end_writeback);
+
+/**
+ * __folio_lock - Get a lock on the folio, assuming we need to sleep to get it.
+ * @folio: The folio to lock
+ */
+void __folio_lock(struct folio *folio)
+{
+	folio_wait_bit_common(folio, PG_locked, TASK_UNINTERRUPTIBLE,
+				EXCLUSIVE);
+}
+EXPORT_SYMBOL(__folio_lock);
+
+int __folio_lock_killable(struct folio *folio)
+{
+	return folio_wait_bit_common(folio, PG_locked, TASK_KILLABLE,
+					EXCLUSIVE);
+}
+EXPORT_SYMBOL_GPL(__folio_lock_killable);
+
+static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
+{
+	struct wait_queue_head *q = folio_waitqueue(folio);
+	int ret = 0;
+
+	wait->folio = folio;
+	wait->bit_nr = PG_locked;
+
+	spin_lock_irq(&q->lock);
+	__add_wait_queue_entry_tail(q, &wait->wait);
+	folio_set_waiters(folio);
+	ret = !folio_trylock(folio);
+	/*
+	 * If we were successful now, we know we're still on the
+	 * waitqueue as we're still under the lock. This means it's
+	 * safe to remove and return success, we know the callback
+	 * isn't going to trigger.
+	 */
+	if (!ret)
+		__remove_wait_queue(q, &wait->wait);
+	else
+		ret = -EIOCBQUEUED;
+	spin_unlock_irq(&q->lock);
+	return ret;
+}
+
+/*
+ * Return values:
+ * 0 - folio is locked.
+ * non-zero - folio is not locked.
+ *     mmap_lock or per-VMA lock has been released (mmap_read_unlock() or
+ *     vma_end_read()), unless flags had both FAULT_FLAG_ALLOW_RETRY and
+ *     FAULT_FLAG_RETRY_NOWAIT set, in which case the lock is still held.
+ *
+ * If neither ALLOW_RETRY nor KILLABLE are set, will always return 0
+ * with the folio locked and the mmap_lock/per-VMA lock is left unperturbed.
+ */
+vm_fault_t __folio_lock_or_retry(struct folio *folio, struct vm_fault *vmf)
+{
+	unsigned int flags = vmf->flags;
+
+	if (fault_flag_allow_retry_first(flags)) {
+		/*
+		 * CAUTION! In this case, mmap_lock/per-VMA lock is not
+		 * released even though returning VM_FAULT_RETRY.
+		 */
+		if (flags & FAULT_FLAG_RETRY_NOWAIT)
+			return VM_FAULT_RETRY;
+
+		release_fault_lock(vmf);
+		if (flags & FAULT_FLAG_KILLABLE)
+			folio_wait_locked_killable(folio);
+		else
+			folio_wait_locked(folio);
+		return VM_FAULT_RETRY;
+	}
+	if (flags & FAULT_FLAG_KILLABLE) {
+		bool ret;
+
+		ret = __folio_lock_killable(folio);
+		if (ret) {
+			release_fault_lock(vmf);
+			return VM_FAULT_RETRY;
+		}
+	} else {
+		__folio_lock(folio);
+	}
+
+	return 0;
+}
+
+/**
+ * page_cache_next_miss() - Find the next gap in the page cache.
+ * @mapping: Mapping.
+ * @index: Index.
+ * @max_scan: Maximum range to search.
+ *
+ * Search the range [index, min(index + max_scan - 1, ULONG_MAX)] for the
+ * gap with the lowest index.
+ *
+ * This function may be called under the rcu_read_lock.  However, this will
+ * not atomically search a snapshot of the cache at a single point in time.
+ * For example, if a gap is created at index 5, then subsequently a gap is
+ * created at index 10, page_cache_next_miss covering both indices may
+ * return 10 if called under the rcu_read_lock.
+ *
+ * Return: The index of the gap if found, otherwise an index outside the
+ * range specified (in which case 'return - index >= max_scan' will be true).
+ * In the rare case of index wrap-around, 0 will be returned.
+ */
+pgoff_t page_cache_next_miss(struct address_space *mapping,
+			     pgoff_t index, unsigned long max_scan)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+
+	while (max_scan--) {
+		void *entry = xas_next(&xas);
+		if (!entry || xa_is_value(entry))
+			break;
+		if (xas.xa_index == 0)
+			break;
+	}
+
+	return xas.xa_index;
+}
+EXPORT_SYMBOL(page_cache_next_miss);
+
+/**
+ * page_cache_prev_miss() - Find the previous gap in the page cache.
+ * @mapping: Mapping.
+ * @index: Index.
+ * @max_scan: Maximum range to search.
+ *
+ * Search the range [max(index - max_scan + 1, 0), index] for the
+ * gap with the highest index.
+ *
+ * This function may be called under the rcu_read_lock.  However, this will
+ * not atomically search a snapshot of the cache at a single point in time.
+ * For example, if a gap is created at index 10, then subsequently a gap is
+ * created at index 5, page_cache_prev_miss() covering both indices may
+ * return 5 if called under the rcu_read_lock.
+ *
+ * Return: The index of the gap if found, otherwise an index outside the
+ * range specified (in which case 'index - return >= max_scan' will be true).
+ * In the rare case of wrap-around, ULONG_MAX will be returned.
+ */
+pgoff_t page_cache_prev_miss(struct address_space *mapping,
+			     pgoff_t index, unsigned long max_scan)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+
+	while (max_scan--) {
+		void *entry = xas_prev(&xas);
+		if (!entry || xa_is_value(entry))
+			break;
+		if (xas.xa_index == ULONG_MAX)
+			break;
+	}
+
+	return xas.xa_index;
+}
+EXPORT_SYMBOL(page_cache_prev_miss);
+
+/*
+ * Lockless page cache protocol:
+ * On the lookup side:
+ * 1. Load the folio from i_pages
+ * 2. Increment the refcount if it's not zero
+ * 3. If the folio is not found by xas_reload(), put the refcount and retry
+ *
+ * On the removal side:
+ * A. Freeze the page (by zeroing the refcount if nobody else has a reference)
+ * B. Remove the page from i_pages
+ * C. Return the page to the page allocator
+ *
+ * This means that any page may have its reference count temporarily
+ * increased by a speculative page cache (or fast GUP) lookup as it can
+ * be allocated by another user before the RCU grace period expires.
+ * Because the refcount temporarily acquired here may end up being the
+ * last refcount on the page, any page allocation must be freeable by
+ * folio_put().
+ */
+
+/*
+ * filemap_get_entry - Get a page cache entry.
+ * @mapping: the address_space to search
+ * @index: The page cache index.
+ *
+ * Looks up the page cache entry at @mapping & @index.  If it is a folio,
+ * it is returned with an increased refcount.  If it is a shadow entry
+ * of a previously evicted folio, or a swap entry from shmem/tmpfs,
+ * it is returned without further action.
+ *
+ * Return: The folio, swap or shadow entry, %NULL if nothing is found.
+ */
+void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	struct folio *folio;
+
+	rcu_read_lock();
+repeat:
+	xas_reset(&xas);
+	folio = xas_load(&xas);
+	if (xas_retry(&xas, folio))
+		goto repeat;
+	/*
+	 * A shadow entry of a recently evicted page, or a swap entry from
+	 * shmem/tmpfs.  Return it without attempting to raise page count.
+	 */
+	if (!folio || xa_is_value(folio))
+		goto out;
+
+	if (!folio_try_get_rcu(folio))
+		goto repeat;
+
+	if (unlikely(folio != xas_reload(&xas))) {
+		folio_put(folio);
+		goto repeat;
+	}
+out:
+	rcu_read_unlock();
+
+	return folio;
+}
+
+/**
+ * __filemap_get_folio - Find and get a reference to a folio.
+ * @mapping: The address_space to search.
+ * @index: The page index.
+ * @fgp_flags: %FGP flags modify how the folio is returned.
+ * @gfp: Memory allocation flags to use if %FGP_CREAT is specified.
+ *
+ * Looks up the page cache entry at @mapping & @index.
+ *
+ * If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
+ * if the %GFP flags specified for %FGP_CREAT are atomic.
+ *
+ * If this function returns a folio, it is returned with an increased refcount.
+ *
+ * Return: The found folio or an ERR_PTR() otherwise.
+ */
+struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
+		fgf_t fgp_flags, gfp_t gfp)
+{
+	struct folio *folio;
+
+repeat:
+	folio = filemap_get_entry(mapping, index);
+	if (xa_is_value(folio))
+		folio = NULL;
+	if (!folio)
+		goto no_page;
+
+	if (fgp_flags & FGP_LOCK) {
+		if (fgp_flags & FGP_NOWAIT) {
+			if (!folio_trylock(folio)) {
+				folio_put(folio);
+				return ERR_PTR(-EAGAIN);
+			}
+		} else {
+			folio_lock(folio);
+		}
+
+		/* Has the page been truncated? */
+		if (unlikely(folio->mapping != mapping)) {
+			folio_unlock(folio);
+			folio_put(folio);
+			goto repeat;
+		}
+		VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
+	}
+
+	if (fgp_flags & FGP_ACCESSED)
+		folio_mark_accessed(folio);
+	else if (fgp_flags & FGP_WRITE) {
+		/* Clear idle flag for buffer write */
+		if (folio_test_idle(folio))
+			folio_clear_idle(folio);
+	}
+
+	if (fgp_flags & FGP_STABLE)
+		folio_wait_stable(folio);
+no_page:
+	if (!folio && (fgp_flags & FGP_CREAT)) {
+		unsigned order = FGF_GET_ORDER(fgp_flags);
+		int err;
+
+		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
+			gfp |= __GFP_WRITE;
+		if (fgp_flags & FGP_NOFS)
+			gfp &= ~__GFP_FS;
+		if (fgp_flags & FGP_NOWAIT) {
+			gfp &= ~GFP_KERNEL;
+			gfp |= GFP_NOWAIT | __GFP_NOWARN;
+		}
+		if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
+			fgp_flags |= FGP_LOCK;
+
+		if (!mapping_large_folio_support(mapping))
+			order = 0;
+		if (order > MAX_PAGECACHE_ORDER)
+			order = MAX_PAGECACHE_ORDER;
+		/* If we're not aligned, allocate a smaller folio */
+		if (index & ((1UL << order) - 1))
+			order = __ffs(index);
+
+		do {
+			gfp_t alloc_gfp = gfp;
+
+			err = -ENOMEM;
+			if (order == 1)
+				order = 0;
+			if (order > 0)
+				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
+			folio = filemap_alloc_folio(alloc_gfp, order);
+			if (!folio)
+				continue;
+
+			/* Init accessed so avoid atomic mark_page_accessed later */
+			if (fgp_flags & FGP_ACCESSED)
+				__folio_set_referenced(folio);
+
+			err = filemap_add_folio(mapping, folio, index, gfp);
+			if (!err)
+				break;
+			folio_put(folio);
+			folio = NULL;
+		} while (order-- > 0);
+
+		if (err == -EEXIST)
+			goto repeat;
+		if (err)
+			return ERR_PTR(err);
+		/*
+		 * filemap_add_folio locks the page, and for mmap
+		 * we expect an unlocked page.
+		 */
+		if (folio && (fgp_flags & FGP_FOR_MMAP))
+			folio_unlock(folio);
+	}
+
+	if (!folio)
+		return ERR_PTR(-ENOENT);
+	return folio;
+}
+EXPORT_SYMBOL(__filemap_get_folio);
+
+static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
+		xa_mark_t mark)
+{
+	struct folio *folio;
+
+retry:
+	if (mark == XA_PRESENT)
+		folio = xas_find(xas, max);
+	else
+		folio = xas_find_marked(xas, max, mark);
+
+	if (xas_retry(xas, folio))
+		goto retry;
+	/*
+	 * A shadow entry of a recently evicted page, a swap
+	 * entry from shmem/tmpfs or a DAX entry.  Return it
+	 * without attempting to raise page count.
+	 */
+	if (!folio || xa_is_value(folio))
+		return folio;
+
+	if (!folio_try_get_rcu(folio))
+		goto reset;
+
+	if (unlikely(folio != xas_reload(xas))) {
+		folio_put(folio);
+		goto reset;
+	}
+
+	return folio;
+reset:
+	xas_reset(xas);
+	goto retry;
+}
+
+/**
+ * find_get_entries - gang pagecache lookup
+ * @mapping:	The address_space to search
+ * @start:	The starting page cache index
+ * @end:	The final page index (inclusive).
+ * @fbatch:	Where the resulting entries are placed.
+ * @indices:	The cache indices corresponding to the entries in @entries
+ *
+ * find_get_entries() will search for and return a batch of entries in
+ * the mapping.  The entries are placed in @fbatch.  find_get_entries()
+ * takes a reference on any actual folios it returns.
+ *
+ * The entries have ascending indexes.  The indices may not be consecutive
+ * due to not-present entries or large folios.
+ *
+ * Any shadow entries of evicted folios, or swap entries from
+ * shmem/tmpfs, are included in the returned array.
+ *
+ * Return: The number of entries which were found.
+ */
+unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
+		pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct folio *folio;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
+		indices[fbatch->nr] = xas.xa_index;
+		if (!folio_batch_add(fbatch, folio))
+			break;
+	}
+	rcu_read_unlock();
+
+	if (folio_batch_count(fbatch)) {
+		unsigned long nr = 1;
+		int idx = folio_batch_count(fbatch) - 1;
+
+		folio = fbatch->folios[idx];
+		if (!xa_is_value(folio) && !folio_test_hugetlb(folio))
+			nr = folio_nr_pages(folio);
+		*start = indices[idx] + nr;
+	}
+	return folio_batch_count(fbatch);
+}
+
+/**
+ * find_lock_entries - Find a batch of pagecache entries.
+ * @mapping:	The address_space to search.
+ * @start:	The starting page cache index.
+ * @end:	The final page index (inclusive).
+ * @fbatch:	Where the resulting entries are placed.
+ * @indices:	The cache indices of the entries in @fbatch.
+ *
+ * find_lock_entries() will return a batch of entries from @mapping.
+ * Swap, shadow and DAX entries are included.  Folios are returned
+ * locked and with an incremented refcount.  Folios which are locked
+ * by somebody else or under writeback are skipped.  Folios which are
+ * partially outside the range are not returned.
+ *
+ * The entries have ascending indexes.  The indices may not be consecutive
+ * due to not-present entries, large folios, folios which could not be
+ * locked or folios under writeback.
+ *
+ * Return: The number of entries which were found.
+ */
+unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
+		pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct folio *folio;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, end, XA_PRESENT))) {
+		if (!xa_is_value(folio)) {
+			if (folio->index < *start)
+				goto put;
+			if (folio_next_index(folio) - 1 > end)
+				goto put;
+			if (!folio_trylock(folio))
+				goto put;
+			if (folio->mapping != mapping ||
+			    folio_test_writeback(folio))
+				goto unlock;
+			VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index),
+					folio);
+		}
+		indices[fbatch->nr] = xas.xa_index;
+		if (!folio_batch_add(fbatch, folio))
+			break;
+		continue;
+unlock:
+		folio_unlock(folio);
+put:
+		folio_put(folio);
+	}
+	rcu_read_unlock();
+
+	if (folio_batch_count(fbatch)) {
+		unsigned long nr = 1;
+		int idx = folio_batch_count(fbatch) - 1;
+
+		folio = fbatch->folios[idx];
+		if (!xa_is_value(folio) && !folio_test_hugetlb(folio))
+			nr = folio_nr_pages(folio);
+		*start = indices[idx] + nr;
+	}
+	return folio_batch_count(fbatch);
+}
+
+/**
+ * filemap_get_folios - Get a batch of folios
+ * @mapping:	The address_space to search
+ * @start:	The starting page index
+ * @end:	The final page index (inclusive)
+ * @fbatch:	The batch to fill.
+ *
+ * Search for and return a batch of folios in the mapping starting at
+ * index @start and up to index @end (inclusive).  The folios are returned
+ * in @fbatch with an elevated reference count.
+ *
+ * The first folio may start before @start; if it does, it will contain
+ * @start.  The final folio may extend beyond @end; if it does, it will
+ * contain @end.  The folios have ascending indices.  There may be gaps
+ * between the folios if there are indices which have no folio in the
+ * page cache.  If folios are added to or removed from the page cache
+ * while this is running, they may or may not be found by this call.
+ *
+ * Return: The number of folios which were found.
+ * We also update @start to index the next folio for the traversal.
+ */
+unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
+		pgoff_t end, struct folio_batch *fbatch)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct folio *folio;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
+		/* Skip over shadow, swap and DAX entries */
+		if (xa_is_value(folio))
+			continue;
+		if (!folio_batch_add(fbatch, folio)) {
+			unsigned long nr = folio_nr_pages(folio);
+
+			if (folio_test_hugetlb(folio))
+				nr = 1;
+			*start = folio->index + nr;
+			goto out;
+		}
+	}
+
+	/*
+	 * We come here when there is no page beyond @end. We take care to not
+	 * overflow the index @start as it confuses some of the callers. This
+	 * breaks the iteration when there is a page at index -1 but that is
+	 * already broken anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*start = (pgoff_t)-1;
+	else
+		*start = end + 1;
+out:
+	rcu_read_unlock();
+
+	return folio_batch_count(fbatch);
+}
+EXPORT_SYMBOL(filemap_get_folios);
+
+/**
+ * filemap_get_folios_contig - Get a batch of contiguous folios
+ * @mapping:	The address_space to search
+ * @start:	The starting page index
+ * @end:	The final page index (inclusive)
+ * @fbatch:	The batch to fill
+ *
+ * filemap_get_folios_contig() works exactly like filemap_get_folios(),
+ * except the returned folios are guaranteed to be contiguous. This may
+ * not return all contiguous folios if the batch gets filled up.
+ *
+ * Return: The number of folios found.
+ * Also update @start to be positioned for traversal of the next folio.
+ */
+
+unsigned filemap_get_folios_contig(struct address_space *mapping,
+		pgoff_t *start, pgoff_t end, struct folio_batch *fbatch)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	unsigned long nr;
+	struct folio *folio;
+
+	rcu_read_lock();
+
+	for (folio = xas_load(&xas); folio && xas.xa_index <= end;
+			folio = xas_next(&xas)) {
+		if (xas_retry(&xas, folio))
+			continue;
+		/*
+		 * If the entry has been swapped out, we can stop looking.
+		 * No current caller is looking for DAX entries.
+		 */
+		if (xa_is_value(folio))
+			goto update_start;
+
+		if (!folio_try_get_rcu(folio))
+			goto retry;
+
+		if (unlikely(folio != xas_reload(&xas)))
+			goto put_folio;
+
+		if (!folio_batch_add(fbatch, folio)) {
+			nr = folio_nr_pages(folio);
+
+			if (folio_test_hugetlb(folio))
+				nr = 1;
+			*start = folio->index + nr;
+			goto out;
+		}
+		continue;
+put_folio:
+		folio_put(folio);
+
+retry:
+		xas_reset(&xas);
+	}
+
+update_start:
+	nr = folio_batch_count(fbatch);
+
+	if (nr) {
+		folio = fbatch->folios[nr - 1];
+		if (folio_test_hugetlb(folio))
+			*start = folio->index + 1;
+		else
+			*start = folio_next_index(folio);
+	}
+out:
+	rcu_read_unlock();
+	return folio_batch_count(fbatch);
+}
+EXPORT_SYMBOL(filemap_get_folios_contig);
+
+/**
+ * filemap_get_folios_tag - Get a batch of folios matching @tag
+ * @mapping:    The address_space to search
+ * @start:      The starting page index
+ * @end:        The final page index (inclusive)
+ * @tag:        The tag index
+ * @fbatch:     The batch to fill
+ *
+ * Same as filemap_get_folios(), but only returning folios tagged with @tag.
+ *
+ * Return: The number of folios found.
+ * Also update @start to index the next folio for traversal.
+ */
+unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
+			pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct folio *folio;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, end, tag)) != NULL) {
+		/*
+		 * Shadow entries should never be tagged, but this iteration
+		 * is lockless so there is a window for page reclaim to evict
+		 * a page we saw tagged. Skip over it.
+		 */
+		if (xa_is_value(folio))
+			continue;
+		if (!folio_batch_add(fbatch, folio)) {
+			unsigned long nr = folio_nr_pages(folio);
+
+			if (folio_test_hugetlb(folio))
+				nr = 1;
+			*start = folio->index + nr;
+			goto out;
+		}
+	}
+	/*
+	 * We come here when there is no page beyond @end. We take care to not
+	 * overflow the index @start as it confuses some of the callers. This
+	 * breaks the iteration when there is a page at index -1 but that is
+	 * already broke anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*start = (pgoff_t)-1;
+	else
+		*start = end + 1;
+out:
+	rcu_read_unlock();
+
+	return folio_batch_count(fbatch);
+}
+EXPORT_SYMBOL(filemap_get_folios_tag);
+
+/*
+ * CD/DVDs are error prone. When a medium error occurs, the driver may fail
+ * a _large_ part of the i/o request. Imagine the worst scenario:
+ *
+ *      ---R__________________________________________B__________
+ *         ^ reading here                             ^ bad block(assume 4k)
+ *
+ * read(R) => miss => readahead(R...B) => media error => frustrating retries
+ * => failing the whole request => read(R) => read(R+1) =>
+ * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
+ * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
+ * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
+ *
+ * It is going insane. Fix it by quickly scaling down the readahead size.
+ */
+static void shrink_readahead_size_eio(struct file_ra_state *ra)
+{
+	ra->ra_pages /= 4;
+}
+
+/*
+ * filemap_get_read_batch - Get a batch of folios for read
+ *
+ * Get a batch of folios which represent a contiguous range of bytes in
+ * the file.  No exceptional entries will be returned.  If @index is in
+ * the middle of a folio, the entire folio will be returned.  The last
+ * folio in the batch may have the readahead flag set or the uptodate flag
+ * clear so that the caller can take the appropriate action.
+ */
+static void filemap_get_read_batch(struct address_space *mapping,
+		pgoff_t index, pgoff_t max, struct folio_batch *fbatch)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	struct folio *folio;
+
+	rcu_read_lock();
+	for (folio = xas_load(&xas); folio; folio = xas_next(&xas)) {
+		if (xas_retry(&xas, folio))
+			continue;
+		if (xas.xa_index > max || xa_is_value(folio))
+			break;
+		if (xa_is_sibling(folio))
+			break;
+		if (!folio_try_get_rcu(folio))
+			goto retry;
+
+		if (unlikely(folio != xas_reload(&xas)))
+			goto put_folio;
+
+		if (!folio_batch_add(fbatch, folio))
+			break;
+		if (!folio_test_uptodate(folio))
+			break;
+		if (folio_test_readahead(folio))
+			break;
+		xas_advance(&xas, folio_next_index(folio) - 1);
+		continue;
+put_folio:
+		folio_put(folio);
+retry:
+		xas_reset(&xas);
+	}
+	rcu_read_unlock();
+}
+
+static int filemap_read_folio(struct file *file, filler_t filler,
+		struct folio *folio)
+{
+	bool workingset = folio_test_workingset(folio);
+	unsigned long pflags;
+	int error;
+
+	/*
+	 * A previous I/O error may have been due to temporary failures,
+	 * eg. multipath errors.  PG_error will be set again if read_folio
+	 * fails.
+	 */
+	folio_clear_error(folio);
+
+	/* Start the actual read. The read will unlock the page. */
+	if (unlikely(workingset))
+		psi_memstall_enter(&pflags);
+	error = filler(file, folio);
+	if (unlikely(workingset))
+		psi_memstall_leave(&pflags);
+	if (error)
+		return error;
+
+	error = folio_wait_locked_killable(folio);
+	if (error)
+		return error;
+	if (folio_test_uptodate(folio))
+		return 0;
+	if (file)
+		shrink_readahead_size_eio(&file->f_ra);
+	return -EIO;
+}
+
+static bool filemap_range_uptodate(struct address_space *mapping,
+		loff_t pos, size_t count, struct folio *folio,
+		bool need_uptodate)
+{
+	if (folio_test_uptodate(folio))
+		return true;
+	/* pipes can't handle partially uptodate pages */
+	if (need_uptodate)
+		return false;
+	if (!mapping->a_ops->is_partially_uptodate)
+		return false;
+	if (mapping->host->i_blkbits >= folio_shift(folio))
+		return false;
+
+	if (folio_pos(folio) > pos) {
+		count -= folio_pos(folio) - pos;
+		pos = 0;
+	} else {
+		pos -= folio_pos(folio);
+	}
+
+	return mapping->a_ops->is_partially_uptodate(folio, pos, count);
+}
+
+static int filemap_update_page(struct kiocb *iocb,
+		struct address_space *mapping, size_t count,
+		struct folio *folio, bool need_uptodate)
+{
+	int error;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!filemap_invalidate_trylock_shared(mapping))
+			return -EAGAIN;
+	} else {
+		filemap_invalidate_lock_shared(mapping);
+	}
+
+	if (!folio_trylock(folio)) {
+		error = -EAGAIN;
+		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
+			goto unlock_mapping;
+		if (!(iocb->ki_flags & IOCB_WAITQ)) {
+			filemap_invalidate_unlock_shared(mapping);
+			/*
+			 * This is where we usually end up waiting for a
+			 * previously submitted readahead to finish.
+			 */
+			folio_put_wait_locked(folio, TASK_KILLABLE);
+			return AOP_TRUNCATED_PAGE;
+		}
+		error = __folio_lock_async(folio, iocb->ki_waitq);
+		if (error)
+			goto unlock_mapping;
+	}
+
+	error = AOP_TRUNCATED_PAGE;
+	if (!folio->mapping)
+		goto unlock;
+
+	error = 0;
+	if (filemap_range_uptodate(mapping, iocb->ki_pos, count, folio,
+				   need_uptodate))
+		goto unlock;
+
+	error = -EAGAIN;
+	if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
+		goto unlock;
+
+	error = filemap_read_folio(iocb->ki_filp, mapping->a_ops->read_folio,
+			folio);
+	goto unlock_mapping;
+unlock:
+	folio_unlock(folio);
+unlock_mapping:
+	filemap_invalidate_unlock_shared(mapping);
+	if (error == AOP_TRUNCATED_PAGE)
+		folio_put(folio);
+	return error;
+}
+
+static int filemap_create_folio(struct file *file,
+		struct address_space *mapping, pgoff_t index,
+		struct folio_batch *fbatch)
+{
+	struct folio *folio;
+	int error;
+
+	folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
+	if (!folio)
+		return -ENOMEM;
+
+	/*
+	 * Protect against truncate / hole punch. Grabbing invalidate_lock
+	 * here assures we cannot instantiate and bring uptodate new
+	 * pagecache folios after evicting page cache during truncate
+	 * and before actually freeing blocks.	Note that we could
+	 * release invalidate_lock after inserting the folio into
+	 * the page cache as the locked folio would then be enough to
+	 * synchronize with hole punching. But there are code paths
+	 * such as filemap_update_page() filling in partially uptodate
+	 * pages or ->readahead() that need to hold invalidate_lock
+	 * while mapping blocks for IO so let's hold the lock here as
+	 * well to keep locking rules simple.
+	 */
+	filemap_invalidate_lock_shared(mapping);
+	error = filemap_add_folio(mapping, folio, index,
+			mapping_gfp_constraint(mapping, GFP_KERNEL));
+	if (error == -EEXIST)
+		error = AOP_TRUNCATED_PAGE;
+	if (error)
+		goto error;
+
+	error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
+	if (error)
+		goto error;
+
+	filemap_invalidate_unlock_shared(mapping);
+	folio_batch_add(fbatch, folio);
+	return 0;
+error:
+	filemap_invalidate_unlock_shared(mapping);
+	folio_put(folio);
+	return error;
+}
+
+static int filemap_readahead(struct kiocb *iocb, struct file *file,
+		struct address_space *mapping, struct folio *folio,
+		pgoff_t last_index)
+{
+	DEFINE_READAHEAD(ractl, file, &file->f_ra, mapping, folio->index);
+
+	if (iocb->ki_flags & IOCB_NOIO)
+		return -EAGAIN;
+	page_cache_async_ra(&ractl, folio, last_index - folio->index);
+	return 0;
+}
+
+static int filemap_get_pages(struct kiocb *iocb, size_t count,
+		struct folio_batch *fbatch, bool need_uptodate)
+{
+	struct file *filp = iocb->ki_filp;
+	struct address_space *mapping = filp->f_mapping;
+	struct file_ra_state *ra = &filp->f_ra;
+	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
+	pgoff_t last_index;
+	struct folio *folio;
+	int err = 0;
+
+	/* "last_index" is the index of the page beyond the end of the read */
+	last_index = DIV_ROUND_UP(iocb->ki_pos + count, PAGE_SIZE);
+retry:
+	if (fatal_signal_pending(current))
+		return -EINTR;
+
+	filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
+	if (!folio_batch_count(fbatch)) {
+		if (iocb->ki_flags & IOCB_NOIO)
+			return -EAGAIN;
+		page_cache_sync_readahead(mapping, ra, filp, index,
+				last_index - index);
+		filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
+	}
+	if (!folio_batch_count(fbatch)) {
+		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
+			return -EAGAIN;
+		err = filemap_create_folio(filp, mapping,
+				iocb->ki_pos >> PAGE_SHIFT, fbatch);
+		if (err == AOP_TRUNCATED_PAGE)
+			goto retry;
+		return err;
+	}
+
+	folio = fbatch->folios[folio_batch_count(fbatch) - 1];
+	if (folio_test_readahead(folio)) {
+		err = filemap_readahead(iocb, filp, mapping, folio, last_index);
+		if (err)
+			goto err;
+	}
+	if (!folio_test_uptodate(folio)) {
+		if ((iocb->ki_flags & IOCB_WAITQ) &&
+		    folio_batch_count(fbatch) > 1)
+			iocb->ki_flags |= IOCB_NOWAIT;
+		err = filemap_update_page(iocb, mapping, count, folio,
+					  need_uptodate);
+		if (err)
+			goto err;
+	}
+
+	return 0;
+err:
+	if (err < 0)
+		folio_put(folio);
+	if (likely(--fbatch->nr))
+		return 0;
+	if (err == AOP_TRUNCATED_PAGE)
+		goto retry;
+	return err;
+}
+
+static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
+{
+	unsigned int shift = folio_shift(folio);
+
+	return (pos1 >> shift == pos2 >> shift);
+}
+
+/**
+ * filemap_read - Read data from the page cache.
+ * @iocb: The iocb to read.
+ * @iter: Destination for the data.
+ * @already_read: Number of bytes already read by the caller.
+ *
+ * Copies data from the page cache.  If the data is not currently present,
+ * uses the readahead and read_folio address_space operations to fetch it.
+ *
+ * Return: Total number of bytes copied, including those already read by
+ * the caller.  If an error happens before any bytes are copied, returns
+ * a negative error number.
+ */
+ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
+		ssize_t already_read)
+{
+	struct file *filp = iocb->ki_filp;
+	struct file_ra_state *ra = &filp->f_ra;
+	struct address_space *mapping = filp->f_mapping;
+	struct inode *inode = mapping->host;
+	struct folio_batch fbatch;
+	int i, error = 0;
+	bool writably_mapped;
+	loff_t isize, end_offset;
+	loff_t last_pos = ra->prev_pos;
+
+	if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
+		return 0;
+	if (unlikely(!iov_iter_count(iter)))
+		return 0;
+
+	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+	folio_batch_init(&fbatch);
+
+	do {
+		cond_resched();
+
+		/*
+		 * If we've already successfully copied some data, then we
+		 * can no longer safely return -EIOCBQUEUED. Hence mark
+		 * an async read NOWAIT at that point.
+		 */
+		if ((iocb->ki_flags & IOCB_WAITQ) && already_read)
+			iocb->ki_flags |= IOCB_NOWAIT;
+
+		if (unlikely(iocb->ki_pos >= i_size_read(inode)))
+			break;
+
+		error = filemap_get_pages(iocb, iter->count, &fbatch, false);
+		if (error < 0)
+			break;
+
+		/*
+		 * i_size must be checked after we know the pages are Uptodate.
+		 *
+		 * Checking i_size after the check allows us to calculate
+		 * the correct value for "nr", which means the zero-filled
+		 * part of the page is not copied back to userspace (unless
+		 * another truncate extends the file - this is desired though).
+		 */
+		isize = i_size_read(inode);
+		if (unlikely(iocb->ki_pos >= isize))
+			goto put_folios;
+		end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
+
+		/*
+		 * Pairs with a barrier in
+		 * block_write_end()->mark_buffer_dirty() or other page
+		 * dirtying routines like iomap_write_end() to ensure
+		 * changes to page contents are visible before we see
+		 * increased inode size.
+		 */
+		smp_rmb();
+
+		/*
+		 * Once we start copying data, we don't want to be touching any
+		 * cachelines that might be contended:
+		 */
+		writably_mapped = mapping_writably_mapped(mapping);
+
+		/*
+		 * When a read accesses the same folio several times, only
+		 * mark it as accessed the first time.
+		 */
+		if (!pos_same_folio(iocb->ki_pos, last_pos - 1,
+				    fbatch.folios[0]))
+			folio_mark_accessed(fbatch.folios[0]);
+
+		for (i = 0; i < folio_batch_count(&fbatch); i++) {
+			struct folio *folio = fbatch.folios[i];
+			size_t fsize = folio_size(folio);
+			size_t offset = iocb->ki_pos & (fsize - 1);
+			size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos,
+					     fsize - offset);
+			size_t copied;
+
+			if (end_offset < folio_pos(folio))
+				break;
+			if (i > 0)
+				folio_mark_accessed(folio);
+			/*
+			 * If users can be writing to this folio using arbitrary
+			 * virtual addresses, take care of potential aliasing
+			 * before reading the folio on the kernel side.
+			 */
+			if (writably_mapped)
+				flush_dcache_folio(folio);
+
+			copied = copy_folio_to_iter(folio, offset, bytes, iter);
+
+			already_read += copied;
+			iocb->ki_pos += copied;
+			last_pos = iocb->ki_pos;
+
+			if (copied < bytes) {
+				error = -EFAULT;
+				break;
+			}
+		}
+put_folios:
+		for (i = 0; i < folio_batch_count(&fbatch); i++)
+			folio_put(fbatch.folios[i]);
+		folio_batch_init(&fbatch);
+	} while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
+
+	file_accessed(filp);
+	ra->prev_pos = last_pos;
+	return already_read ? already_read : error;
+}
+EXPORT_SYMBOL_GPL(filemap_read);
+
+int kiocb_write_and_wait(struct kiocb *iocb, size_t count)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	loff_t pos = iocb->ki_pos;
+	loff_t end = pos + count - 1;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (filemap_range_needs_writeback(mapping, pos, end))
+			return -EAGAIN;
+		return 0;
+	}
+
+	return filemap_write_and_wait_range(mapping, pos, end);
+}
+
+int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	loff_t pos = iocb->ki_pos;
+	loff_t end = pos + count - 1;
+	int ret;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		/* we could block if there are any pages in the range */
+		if (filemap_range_has_page(mapping, pos, end))
+			return -EAGAIN;
+	} else {
+		ret = filemap_write_and_wait_range(mapping, pos, end);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * After a write we want buffered reads to be sure to go to disk to get
+	 * the new data.  We invalidate clean cached page from the region we're
+	 * about to write.  We do this *before* the write so that we can return
+	 * without clobbering -EIOCBQUEUED from ->direct_IO().
+	 */
+	return invalidate_inode_pages2_range(mapping, pos >> PAGE_SHIFT,
+					     end >> PAGE_SHIFT);
+}
+
+/**
+ * generic_file_read_iter - generic filesystem read routine
+ * @iocb:	kernel I/O control block
+ * @iter:	destination for the data read
+ *
+ * This is the "read_iter()" routine for all filesystems
+ * that can use the page cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
+ * be returned when no data can be read without waiting for I/O requests
+ * to complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
+ * requests shall be made for the read or for readahead.  When no data
+ * can be read, -EAGAIN shall be returned.  When readahead would be
+ * triggered, a partial, possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t
+generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	size_t count = iov_iter_count(iter);
+	ssize_t retval = 0;
+
+	if (!count)
+		return 0; /* skip atime */
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		struct file *file = iocb->ki_filp;
+		struct address_space *mapping = file->f_mapping;
+		struct inode *inode = mapping->host;
+
+		retval = kiocb_write_and_wait(iocb, count);
+		if (retval < 0)
+			return retval;
+		file_accessed(file);
+
+		retval = mapping->a_ops->direct_IO(iocb, iter);
+		if (retval >= 0) {
+			iocb->ki_pos += retval;
+			count -= retval;
+		}
+		if (retval != -EIOCBQUEUED)
+			iov_iter_revert(iter, count - iov_iter_count(iter));
+
+		/*
+		 * Btrfs can have a short DIO read if we encounter
+		 * compressed extents, so if there was an error, or if
+		 * we've already read everything we wanted to, or if
+		 * there was a short read because we hit EOF, go ahead
+		 * and return.  Otherwise fallthrough to buffered io for
+		 * the rest of the read.  Buffered reads will not work for
+		 * DAX files, so don't bother trying.
+		 */
+		if (retval < 0 || !count || IS_DAX(inode))
+			return retval;
+		if (iocb->ki_pos >= i_size_read(inode))
+			return retval;
+	}
+
+	return filemap_read(iocb, iter, retval);
+}
+EXPORT_SYMBOL(generic_file_read_iter);
+
+/*
+ * Splice subpages from a folio into a pipe.
+ */
+size_t splice_folio_into_pipe(struct pipe_inode_info *pipe,
+			      struct folio *folio, loff_t fpos, size_t size)
+{
+	struct page *page;
+	size_t spliced = 0, offset = offset_in_folio(folio, fpos);
+
+	page = folio_page(folio, offset / PAGE_SIZE);
+	size = min(size, folio_size(folio) - offset);
+	offset %= PAGE_SIZE;
+
+	while (spliced < size &&
+	       !pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
+		struct pipe_buffer *buf = pipe_head_buf(pipe);
+		size_t part = min_t(size_t, PAGE_SIZE - offset, size - spliced);
+
+		*buf = (struct pipe_buffer) {
+			.ops	= &page_cache_pipe_buf_ops,
+			.page	= page,
+			.offset	= offset,
+			.len	= part,
+		};
+		folio_get(folio);
+		pipe->head++;
+		page++;
+		spliced += part;
+		offset = 0;
+	}
+
+	return spliced;
+}
+
+/**
+ * filemap_splice_read -  Splice data from a file's pagecache into a pipe
+ * @in: The file to read from
+ * @ppos: Pointer to the file position to read from
+ * @pipe: The pipe to splice into
+ * @len: The amount to splice
+ * @flags: The SPLICE_F_* flags
+ *
+ * This function gets folios from a file's pagecache and splices them into the
+ * pipe.  Readahead will be called as necessary to fill more folios.  This may
+ * be used for blockdevs also.
+ *
+ * Return: On success, the number of bytes read will be returned and *@ppos
+ * will be updated if appropriate; 0 will be returned if there is no more data
+ * to be read; -EAGAIN will be returned if the pipe had no space, and some
+ * other negative error code will be returned on error.  A short read may occur
+ * if the pipe has insufficient space, we reach the end of the data or we hit a
+ * hole.
+ */
+ssize_t filemap_splice_read(struct file *in, loff_t *ppos,
+			    struct pipe_inode_info *pipe,
+			    size_t len, unsigned int flags)
+{
+	struct folio_batch fbatch;
+	struct kiocb iocb;
+	size_t total_spliced = 0, used, npages;
+	loff_t isize, end_offset;
+	bool writably_mapped;
+	int i, error = 0;
+
+	if (unlikely(*ppos >= in->f_mapping->host->i_sb->s_maxbytes))
+		return 0;
+
+	init_sync_kiocb(&iocb, in);
+	iocb.ki_pos = *ppos;
+
+	/* Work out how much data we can actually add into the pipe */
+	used = pipe_occupancy(pipe->head, pipe->tail);
+	npages = max_t(ssize_t, pipe->max_usage - used, 0);
+	len = min_t(size_t, len, npages * PAGE_SIZE);
+
+	folio_batch_init(&fbatch);
+
+	do {
+		cond_resched();
+
+		if (*ppos >= i_size_read(in->f_mapping->host))
+			break;
+
+		iocb.ki_pos = *ppos;
+		error = filemap_get_pages(&iocb, len, &fbatch, true);
+		if (error < 0)
+			break;
+
+		/*
+		 * i_size must be checked after we know the pages are Uptodate.
+		 *
+		 * Checking i_size after the check allows us to calculate
+		 * the correct value for "nr", which means the zero-filled
+		 * part of the page is not copied back to userspace (unless
+		 * another truncate extends the file - this is desired though).
+		 */
+		isize = i_size_read(in->f_mapping->host);
+		if (unlikely(*ppos >= isize))
+			break;
+		end_offset = min_t(loff_t, isize, *ppos + len);
+
+		/*
+		 * Once we start copying data, we don't want to be touching any
+		 * cachelines that might be contended:
+		 */
+		writably_mapped = mapping_writably_mapped(in->f_mapping);
+
+		for (i = 0; i < folio_batch_count(&fbatch); i++) {
+			struct folio *folio = fbatch.folios[i];
+			size_t n;
+
+			if (folio_pos(folio) >= end_offset)
+				goto out;
+			folio_mark_accessed(folio);
+
+			/*
+			 * If users can be writing to this folio using arbitrary
+			 * virtual addresses, take care of potential aliasing
+			 * before reading the folio on the kernel side.
+			 */
+			if (writably_mapped)
+				flush_dcache_folio(folio);
+
+			n = min_t(loff_t, len, isize - *ppos);
+			n = splice_folio_into_pipe(pipe, folio, *ppos, n);
+			if (!n)
+				goto out;
+			len -= n;
+			total_spliced += n;
+			*ppos += n;
+			in->f_ra.prev_pos = *ppos;
+			if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
+				goto out;
+		}
+
+		folio_batch_release(&fbatch);
+	} while (len);
+
+out:
+	folio_batch_release(&fbatch);
+	file_accessed(in);
+
+	return total_spliced ? total_spliced : error;
+}
+EXPORT_SYMBOL(filemap_splice_read);
+
+static inline loff_t folio_seek_hole_data(struct xa_state *xas,
+		struct address_space *mapping, struct folio *folio,
+		loff_t start, loff_t end, bool seek_data)
+{
+	const struct address_space_operations *ops = mapping->a_ops;
+	size_t offset, bsz = i_blocksize(mapping->host);
+
+	if (xa_is_value(folio) || folio_test_uptodate(folio))
+		return seek_data ? start : end;
+	if (!ops->is_partially_uptodate)
+		return seek_data ? end : start;
+
+	xas_pause(xas);
+	rcu_read_unlock();
+	folio_lock(folio);
+	if (unlikely(folio->mapping != mapping))
+		goto unlock;
+
+	offset = offset_in_folio(folio, start) & ~(bsz - 1);
+
+	do {
+		if (ops->is_partially_uptodate(folio, offset, bsz) ==
+							seek_data)
+			break;
+		start = (start + bsz) & ~(bsz - 1);
+		offset += bsz;
+	} while (offset < folio_size(folio));
+unlock:
+	folio_unlock(folio);
+	rcu_read_lock();
+	return start;
+}
+
+static inline size_t seek_folio_size(struct xa_state *xas, struct folio *folio)
+{
+	if (xa_is_value(folio))
+		return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
+	return folio_size(folio);
+}
+
+/**
+ * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
+ * @mapping: Address space to search.
+ * @start: First byte to consider.
+ * @end: Limit of search (exclusive).
+ * @whence: Either SEEK_HOLE or SEEK_DATA.
+ *
+ * If the page cache knows which blocks contain holes and which blocks
+ * contain data, your filesystem can use this function to implement
+ * SEEK_HOLE and SEEK_DATA.  This is useful for filesystems which are
+ * entirely memory-based such as tmpfs, and filesystems which support
+ * unwritten extents.
+ *
+ * Return: The requested offset on success, or -ENXIO if @whence specifies
+ * SEEK_DATA and there is no data after @start.  There is an implicit hole
+ * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
+ * and @end contain data.
+ */
+loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
+		loff_t end, int whence)
+{
+	XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
+	pgoff_t max = (end - 1) >> PAGE_SHIFT;
+	bool seek_data = (whence == SEEK_DATA);
+	struct folio *folio;
+
+	if (end <= start)
+		return -ENXIO;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, max, XA_PRESENT))) {
+		loff_t pos = (u64)xas.xa_index << PAGE_SHIFT;
+		size_t seek_size;
+
+		if (start < pos) {
+			if (!seek_data)
+				goto unlock;
+			start = pos;
+		}
+
+		seek_size = seek_folio_size(&xas, folio);
+		pos = round_up((u64)pos + 1, seek_size);
+		start = folio_seek_hole_data(&xas, mapping, folio, start, pos,
+				seek_data);
+		if (start < pos)
+			goto unlock;
+		if (start >= end)
+			break;
+		if (seek_size > PAGE_SIZE)
+			xas_set(&xas, pos >> PAGE_SHIFT);
+		if (!xa_is_value(folio))
+			folio_put(folio);
+	}
+	if (seek_data)
+		start = -ENXIO;
+unlock:
+	rcu_read_unlock();
+	if (folio && !xa_is_value(folio))
+		folio_put(folio);
+	if (start > end)
+		return end;
+	return start;
+}
+
+#ifdef CONFIG_MMU
+#define MMAP_LOTSAMISS  (100)
+/*
+ * lock_folio_maybe_drop_mmap - lock the page, possibly dropping the mmap_lock
+ * @vmf - the vm_fault for this fault.
+ * @folio - the folio to lock.
+ * @fpin - the pointer to the file we may pin (or is already pinned).
+ *
+ * This works similar to lock_folio_or_retry in that it can drop the
+ * mmap_lock.  It differs in that it actually returns the folio locked
+ * if it returns 1 and 0 if it couldn't lock the folio.  If we did have
+ * to drop the mmap_lock then fpin will point to the pinned file and
+ * needs to be fput()'ed at a later point.
+ */
+static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio,
+				     struct file **fpin)
+{
+	if (folio_trylock(folio))
+		return 1;
+
+	/*
+	 * NOTE! This will make us return with VM_FAULT_RETRY, but with
+	 * the mmap_lock still held. That's how FAULT_FLAG_RETRY_NOWAIT
+	 * is supposed to work. We have way too many special cases..
+	 */
+	if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+		return 0;
+
+	*fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
+	if (vmf->flags & FAULT_FLAG_KILLABLE) {
+		if (__folio_lock_killable(folio)) {
+			/*
+			 * We didn't have the right flags to drop the mmap_lock,
+			 * but all fault_handlers only check for fatal signals
+			 * if we return VM_FAULT_RETRY, so we need to drop the
+			 * mmap_lock here and return 0 if we don't have a fpin.
+			 */
+			if (*fpin == NULL)
+				mmap_read_unlock(vmf->vma->vm_mm);
+			return 0;
+		}
+	} else
+		__folio_lock(folio);
+
+	return 1;
+}
+
+/*
+ * Synchronous readahead happens when we don't even find a page in the page
+ * cache at all.  We don't want to perform IO under the mmap sem, so if we have
+ * to drop the mmap sem we return the file that was pinned in order for us to do
+ * that.  If we didn't pin a file then we return NULL.  The file that is
+ * returned needs to be fput()'ed when we're done with it.
+ */
+static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct file_ra_state *ra = &file->f_ra;
+	struct address_space *mapping = file->f_mapping;
+	DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
+	struct file *fpin = NULL;
+	unsigned long vm_flags = vmf->vma->vm_flags;
+	unsigned int mmap_miss;
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	/* Use the readahead code, even if readahead is disabled */
+	if (vm_flags & VM_HUGEPAGE) {
+		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+		ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
+		ra->size = HPAGE_PMD_NR;
+		/*
+		 * Fetch two PMD folios, so we get the chance to actually
+		 * readahead, unless we've been told not to.
+		 */
+		if (!(vm_flags & VM_RAND_READ))
+			ra->size *= 2;
+		ra->async_size = HPAGE_PMD_NR;
+		page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
+		return fpin;
+	}
+#endif
+
+	/* If we don't want any read-ahead, don't bother */
+	if (vm_flags & VM_RAND_READ)
+		return fpin;
+	if (!ra->ra_pages)
+		return fpin;
+
+	if (vm_flags & VM_SEQ_READ) {
+		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+		page_cache_sync_ra(&ractl, ra->ra_pages);
+		return fpin;
+	}
+
+	/* Avoid banging the cache line if not needed */
+	mmap_miss = READ_ONCE(ra->mmap_miss);
+	if (mmap_miss < MMAP_LOTSAMISS * 10)
+		WRITE_ONCE(ra->mmap_miss, ++mmap_miss);
+
+	/*
+	 * Do we miss much more than hit in this file? If so,
+	 * stop bothering with read-ahead. It will only hurt.
+	 */
+	if (mmap_miss > MMAP_LOTSAMISS)
+		return fpin;
+
+	/*
+	 * mmap read-around
+	 */
+	fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+	ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
+	ra->size = ra->ra_pages;
+	ra->async_size = ra->ra_pages / 4;
+	ractl._index = ra->start;
+	page_cache_ra_order(&ractl, ra, 0);
+	return fpin;
+}
+
+/*
+ * Asynchronous readahead happens when we find the page and PG_readahead,
+ * so we want to possibly extend the readahead further.  We return the file that
+ * was pinned if we have to drop the mmap_lock in order to do IO.
+ */
+static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
+					    struct folio *folio)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct file_ra_state *ra = &file->f_ra;
+	DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
+	struct file *fpin = NULL;
+	unsigned int mmap_miss;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
+		return fpin;
+
+	mmap_miss = READ_ONCE(ra->mmap_miss);
+	if (mmap_miss)
+		WRITE_ONCE(ra->mmap_miss, --mmap_miss);
+
+	if (folio_test_readahead(folio)) {
+		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+		page_cache_async_ra(&ractl, folio, ra->ra_pages);
+	}
+	return fpin;
+}
+
+/**
+ * filemap_fault - read in file data for page fault handling
+ * @vmf:	struct vm_fault containing details of the fault
+ *
+ * filemap_fault() is invoked via the vma operations vector for a
+ * mapped memory region to read in file data during a page fault.
+ *
+ * The goto's are kind of ugly, but this streamlines the normal case of having
+ * it in the page cache, and handles the special cases reasonably without
+ * having a lot of duplicated code.
+ *
+ * vma->vm_mm->mmap_lock must be held on entry.
+ *
+ * If our return value has VM_FAULT_RETRY set, it's because the mmap_lock
+ * may be dropped before doing I/O or by lock_folio_maybe_drop_mmap().
+ *
+ * If our return value does not have VM_FAULT_RETRY set, the mmap_lock
+ * has not been released.
+ *
+ * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
+ *
+ * Return: bitwise-OR of %VM_FAULT_ codes.
+ */
+vm_fault_t filemap_fault(struct vm_fault *vmf)
+{
+	int error;
+	struct file *file = vmf->vma->vm_file;
+	struct file *fpin = NULL;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	pgoff_t max_idx, index = vmf->pgoff;
+	struct folio *folio;
+	vm_fault_t ret = 0;
+	bool mapping_locked = false;
+
+	max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	if (unlikely(index >= max_idx))
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * Do we have something in the page cache already?
+	 */
+	folio = filemap_get_folio(mapping, index);
+	if (likely(!IS_ERR(folio))) {
+		/*
+		 * We found the page, so try async readahead before waiting for
+		 * the lock.
+		 */
+		if (!(vmf->flags & FAULT_FLAG_TRIED))
+			fpin = do_async_mmap_readahead(vmf, folio);
+		if (unlikely(!folio_test_uptodate(folio))) {
+			filemap_invalidate_lock_shared(mapping);
+			mapping_locked = true;
+		}
+	} else {
+		/* No page in the page cache at all */
+		count_vm_event(PGMAJFAULT);
+		count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
+		ret = VM_FAULT_MAJOR;
+		fpin = do_sync_mmap_readahead(vmf);
+retry_find:
+		/*
+		 * See comment in filemap_create_folio() why we need
+		 * invalidate_lock
+		 */
+		if (!mapping_locked) {
+			filemap_invalidate_lock_shared(mapping);
+			mapping_locked = true;
+		}
+		folio = __filemap_get_folio(mapping, index,
+					  FGP_CREAT|FGP_FOR_MMAP,
+					  vmf->gfp_mask);
+		if (IS_ERR(folio)) {
+			if (fpin)
+				goto out_retry;
+			filemap_invalidate_unlock_shared(mapping);
+			return VM_FAULT_OOM;
+		}
+	}
+
+	if (!lock_folio_maybe_drop_mmap(vmf, folio, &fpin))
+		goto out_retry;
+
+	/* Did it get truncated? */
+	if (unlikely(folio->mapping != mapping)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		goto retry_find;
+	}
+	VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
+
+	/*
+	 * We have a locked page in the page cache, now we need to check
+	 * that it's up-to-date. If not, it is going to be due to an error.
+	 */
+	if (unlikely(!folio_test_uptodate(folio))) {
+		/*
+		 * The page was in cache and uptodate and now it is not.
+		 * Strange but possible since we didn't hold the page lock all
+		 * the time. Let's drop everything get the invalidate lock and
+		 * try again.
+		 */
+		if (!mapping_locked) {
+			folio_unlock(folio);
+			folio_put(folio);
+			goto retry_find;
+		}
+		goto page_not_uptodate;
+	}
+
+	/*
+	 * We've made it this far and we had to drop our mmap_lock, now is the
+	 * time to return to the upper layer and have it re-find the vma and
+	 * redo the fault.
+	 */
+	if (fpin) {
+		folio_unlock(folio);
+		goto out_retry;
+	}
+	if (mapping_locked)
+		filemap_invalidate_unlock_shared(mapping);
+
+	/*
+	 * Found the page and have a reference on it.
+	 * We must recheck i_size under page lock.
+	 */
+	max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	if (unlikely(index >= max_idx)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		return VM_FAULT_SIGBUS;
+	}
+
+	vmf->page = folio_file_page(folio, index);
+	return ret | VM_FAULT_LOCKED;
+
+page_not_uptodate:
+	/*
+	 * Umm, take care of errors if the page isn't up-to-date.
+	 * Try to re-read it _once_. We do this synchronously,
+	 * because there really aren't any performance issues here
+	 * and we need to check for errors.
+	 */
+	fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+	error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
+	if (fpin)
+		goto out_retry;
+	folio_put(folio);
+
+	if (!error || error == AOP_TRUNCATED_PAGE)
+		goto retry_find;
+	filemap_invalidate_unlock_shared(mapping);
+
+	return VM_FAULT_SIGBUS;
+
+out_retry:
+	/*
+	 * We dropped the mmap_lock, we need to return to the fault handler to
+	 * re-find the vma and come back and find our hopefully still populated
+	 * page.
+	 */
+	if (!IS_ERR(folio))
+		folio_put(folio);
+	if (mapping_locked)
+		filemap_invalidate_unlock_shared(mapping);
+	if (fpin)
+		fput(fpin);
+	return ret | VM_FAULT_RETRY;
+}
+EXPORT_SYMBOL(filemap_fault);
+
+static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
+		pgoff_t start)
+{
+	struct mm_struct *mm = vmf->vma->vm_mm;
+
+	/* Huge page is mapped? No need to proceed. */
+	if (pmd_trans_huge(*vmf->pmd)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		return true;
+	}
+
+	if (pmd_none(*vmf->pmd) && folio_test_pmd_mappable(folio)) {
+		struct page *page = folio_file_page(folio, start);
+		vm_fault_t ret = do_set_pmd(vmf, page);
+		if (!ret) {
+			/* The page is mapped successfully, reference consumed. */
+			folio_unlock(folio);
+			return true;
+		}
+	}
+
+	if (pmd_none(*vmf->pmd) && vmf->prealloc_pte)
+		pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
+
+	return false;
+}
+
+static struct folio *next_uptodate_folio(struct xa_state *xas,
+		struct address_space *mapping, pgoff_t end_pgoff)
+{
+	struct folio *folio = xas_next_entry(xas, end_pgoff);
+	unsigned long max_idx;
+
+	do {
+		if (!folio)
+			return NULL;
+		if (xas_retry(xas, folio))
+			continue;
+		if (xa_is_value(folio))
+			continue;
+		if (folio_test_locked(folio))
+			continue;
+		if (!folio_try_get_rcu(folio))
+			continue;
+		/* Has the page moved or been split? */
+		if (unlikely(folio != xas_reload(xas)))
+			goto skip;
+		if (!folio_test_uptodate(folio) || folio_test_readahead(folio))
+			goto skip;
+		if (!folio_trylock(folio))
+			goto skip;
+		if (folio->mapping != mapping)
+			goto unlock;
+		if (!folio_test_uptodate(folio))
+			goto unlock;
+		max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
+		if (xas->xa_index >= max_idx)
+			goto unlock;
+		return folio;
+unlock:
+		folio_unlock(folio);
+skip:
+		folio_put(folio);
+	} while ((folio = xas_next_entry(xas, end_pgoff)) != NULL);
+
+	return NULL;
+}
+
+/*
+ * Map page range [start_page, start_page + nr_pages) of folio.
+ * start_page is gotten from start by folio_page(folio, start)
+ */
+static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
+			struct folio *folio, unsigned long start,
+			unsigned long addr, unsigned int nr_pages,
+			unsigned int *mmap_miss)
+{
+	vm_fault_t ret = 0;
+	struct page *page = folio_page(folio, start);
+	unsigned int count = 0;
+	pte_t *old_ptep = vmf->pte;
+
+	do {
+		if (PageHWPoison(page + count))
+			goto skip;
+
+		(*mmap_miss)++;
+
+		/*
+		 * NOTE: If there're PTE markers, we'll leave them to be
+		 * handled in the specific fault path, and it'll prohibit the
+		 * fault-around logic.
+		 */
+		if (!pte_none(vmf->pte[count]))
+			goto skip;
+
+		count++;
+		continue;
+skip:
+		if (count) {
+			set_pte_range(vmf, folio, page, count, addr);
+			folio_ref_add(folio, count);
+			if (in_range(vmf->address, addr, count * PAGE_SIZE))
+				ret = VM_FAULT_NOPAGE;
+		}
+
+		count++;
+		page += count;
+		vmf->pte += count;
+		addr += count * PAGE_SIZE;
+		count = 0;
+	} while (--nr_pages > 0);
+
+	if (count) {
+		set_pte_range(vmf, folio, page, count, addr);
+		folio_ref_add(folio, count);
+		if (in_range(vmf->address, addr, count * PAGE_SIZE))
+			ret = VM_FAULT_NOPAGE;
+	}
+
+	vmf->pte = old_ptep;
+
+	return ret;
+}
+
+static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
+		struct folio *folio, unsigned long addr,
+		unsigned int *mmap_miss)
+{
+	vm_fault_t ret = 0;
+	struct page *page = &folio->page;
+
+	if (PageHWPoison(page))
+		return ret;
+
+	(*mmap_miss)++;
+
+	/*
+	 * NOTE: If there're PTE markers, we'll leave them to be
+	 * handled in the specific fault path, and it'll prohibit
+	 * the fault-around logic.
+	 */
+	if (!pte_none(ptep_get(vmf->pte)))
+		return ret;
+
+	if (vmf->address == addr)
+		ret = VM_FAULT_NOPAGE;
+
+	set_pte_range(vmf, folio, page, 1, addr);
+	folio_ref_inc(folio);
+
+	return ret;
+}
+
+vm_fault_t filemap_map_pages(struct vm_fault *vmf,
+			     pgoff_t start_pgoff, pgoff_t end_pgoff)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct file *file = vma->vm_file;
+	struct address_space *mapping = file->f_mapping;
+	pgoff_t last_pgoff = start_pgoff;
+	unsigned long addr;
+	XA_STATE(xas, &mapping->i_pages, start_pgoff);
+	struct folio *folio;
+	vm_fault_t ret = 0;
+	unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved;
+
+	rcu_read_lock();
+	folio = next_uptodate_folio(&xas, mapping, end_pgoff);
+	if (!folio)
+		goto out;
+
+	if (filemap_map_pmd(vmf, folio, start_pgoff)) {
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+
+	addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
+	if (!vmf->pte) {
+		folio_unlock(folio);
+		folio_put(folio);
+		goto out;
+	}
+	do {
+		unsigned long end;
+
+		addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
+		vmf->pte += xas.xa_index - last_pgoff;
+		last_pgoff = xas.xa_index;
+		end = folio->index + folio_nr_pages(folio) - 1;
+		nr_pages = min(end, end_pgoff) - xas.xa_index + 1;
+
+		if (!folio_test_large(folio))
+			ret |= filemap_map_order0_folio(vmf,
+					folio, addr, &mmap_miss);
+		else
+			ret |= filemap_map_folio_range(vmf, folio,
+					xas.xa_index - folio->index, addr,
+					nr_pages, &mmap_miss);
+
+		folio_unlock(folio);
+		folio_put(folio);
+	} while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+out:
+	rcu_read_unlock();
+
+	mmap_miss_saved = READ_ONCE(file->f_ra.mmap_miss);
+	if (mmap_miss >= mmap_miss_saved)
+		WRITE_ONCE(file->f_ra.mmap_miss, 0);
+	else
+		WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss_saved - mmap_miss);
+
+	return ret;
+}
+EXPORT_SYMBOL(filemap_map_pages);
+
+vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	struct folio *folio = page_folio(vmf->page);
+	vm_fault_t ret = VM_FAULT_LOCKED;
+
+	sb_start_pagefault(mapping->host->i_sb);
+	file_update_time(vmf->vma->vm_file);
+	folio_lock(folio);
+	if (folio->mapping != mapping) {
+		folio_unlock(folio);
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+	/*
+	 * We mark the folio dirty already here so that when freeze is in
+	 * progress, we are guaranteed that writeback during freezing will
+	 * see the dirty folio and writeprotect it again.
+	 */
+	folio_mark_dirty(folio);
+	folio_wait_stable(folio);
+out:
+	sb_end_pagefault(mapping->host->i_sb);
+	return ret;
+}
+
+const struct vm_operations_struct generic_file_vm_ops = {
+	.fault		= filemap_fault,
+	.map_pages	= filemap_map_pages,
+	.page_mkwrite	= filemap_page_mkwrite,
+};
+
+/* This is used for a general mmap of a disk file */
+
+int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	if (!mapping->a_ops->read_folio)
+		return -ENOEXEC;
+	file_accessed(file);
+	vma->vm_ops = &generic_file_vm_ops;
+	return 0;
+}
+
+/*
+ * This is for filesystems which do not implement ->writepage.
+ */
+int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+		return -EINVAL;
+	return generic_file_mmap(file, vma);
+}
+#else
+vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
+{
+	return VM_FAULT_SIGBUS;
+}
+int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	return -ENOSYS;
+}
+int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	return -ENOSYS;
+}
+#endif /* CONFIG_MMU */
+
+EXPORT_SYMBOL(filemap_page_mkwrite);
+EXPORT_SYMBOL(generic_file_mmap);
+EXPORT_SYMBOL(generic_file_readonly_mmap);
+
+static struct folio *do_read_cache_folio(struct address_space *mapping,
+		pgoff_t index, filler_t filler, struct file *file, gfp_t gfp)
+{
+	struct folio *folio;
+	int err;
+
+	if (!filler)
+		filler = mapping->a_ops->read_folio;
+repeat:
+	folio = filemap_get_folio(mapping, index);
+	if (IS_ERR(folio)) {
+		folio = filemap_alloc_folio(gfp, 0);
+		if (!folio)
+			return ERR_PTR(-ENOMEM);
+		err = filemap_add_folio(mapping, folio, index, gfp);
+		if (unlikely(err)) {
+			folio_put(folio);
+			if (err == -EEXIST)
+				goto repeat;
+			/* Presumably ENOMEM for xarray node */
+			return ERR_PTR(err);
+		}
+
+		goto filler;
+	}
+	if (folio_test_uptodate(folio))
+		goto out;
+
+	if (!folio_trylock(folio)) {
+		folio_put_wait_locked(folio, TASK_UNINTERRUPTIBLE);
+		goto repeat;
+	}
+
+	/* Folio was truncated from mapping */
+	if (!folio->mapping) {
+		folio_unlock(folio);
+		folio_put(folio);
+		goto repeat;
+	}
+
+	/* Someone else locked and filled the page in a very small window */
+	if (folio_test_uptodate(folio)) {
+		folio_unlock(folio);
+		goto out;
+	}
+
+filler:
+	err = filemap_read_folio(file, filler, folio);
+	if (err) {
+		folio_put(folio);
+		if (err == AOP_TRUNCATED_PAGE)
+			goto repeat;
+		return ERR_PTR(err);
+	}
+
+out:
+	folio_mark_accessed(folio);
+	return folio;
+}
+
+/**
+ * read_cache_folio - Read into page cache, fill it if needed.
+ * @mapping: The address_space to read from.
+ * @index: The index to read.
+ * @filler: Function to perform the read, or NULL to use aops->read_folio().
+ * @file: Passed to filler function, may be NULL if not required.
+ *
+ * Read one page into the page cache.  If it succeeds, the folio returned
+ * will contain @index, but it may not be the first page of the folio.
+ *
+ * If the filler function returns an error, it will be returned to the
+ * caller.
+ *
+ * Context: May sleep.  Expects mapping->invalidate_lock to be held.
+ * Return: An uptodate folio on success, ERR_PTR() on failure.
+ */
+struct folio *read_cache_folio(struct address_space *mapping, pgoff_t index,
+		filler_t filler, struct file *file)
+{
+	return do_read_cache_folio(mapping, index, filler, file,
+			mapping_gfp_mask(mapping));
+}
+EXPORT_SYMBOL(read_cache_folio);
+
+/**
+ * mapping_read_folio_gfp - Read into page cache, using specified allocation flags.
+ * @mapping:	The address_space for the folio.
+ * @index:	The index that the allocated folio will contain.
+ * @gfp:	The page allocator flags to use if allocating.
+ *
+ * This is the same as "read_cache_folio(mapping, index, NULL, NULL)", but with
+ * any new memory allocations done using the specified allocation flags.
+ *
+ * The most likely error from this function is EIO, but ENOMEM is
+ * possible and so is EINTR.  If ->read_folio returns another error,
+ * that will be returned to the caller.
+ *
+ * The function expects mapping->invalidate_lock to be already held.
+ *
+ * Return: Uptodate folio on success, ERR_PTR() on failure.
+ */
+struct folio *mapping_read_folio_gfp(struct address_space *mapping,
+		pgoff_t index, gfp_t gfp)
+{
+	return do_read_cache_folio(mapping, index, NULL, NULL, gfp);
+}
+EXPORT_SYMBOL(mapping_read_folio_gfp);
+
+static struct page *do_read_cache_page(struct address_space *mapping,
+		pgoff_t index, filler_t *filler, struct file *file, gfp_t gfp)
+{
+	struct folio *folio;
+
+	folio = do_read_cache_folio(mapping, index, filler, file, gfp);
+	if (IS_ERR(folio))
+		return &folio->page;
+	return folio_file_page(folio, index);
+}
+
+struct page *read_cache_page(struct address_space *mapping,
+			pgoff_t index, filler_t *filler, struct file *file)
+{
+	return do_read_cache_page(mapping, index, filler, file,
+			mapping_gfp_mask(mapping));
+}
+EXPORT_SYMBOL(read_cache_page);
+
+/**
+ * read_cache_page_gfp - read into page cache, using specified page allocation flags.
+ * @mapping:	the page's address_space
+ * @index:	the page index
+ * @gfp:	the page allocator flags to use if allocating
+ *
+ * This is the same as "read_mapping_page(mapping, index, NULL)", but with
+ * any new page allocations done using the specified allocation flags.
+ *
+ * If the page does not get brought uptodate, return -EIO.
+ *
+ * The function expects mapping->invalidate_lock to be already held.
+ *
+ * Return: up to date page on success, ERR_PTR() on failure.
+ */
+struct page *read_cache_page_gfp(struct address_space *mapping,
+				pgoff_t index,
+				gfp_t gfp)
+{
+	return do_read_cache_page(mapping, index, NULL, NULL, gfp);
+}
+EXPORT_SYMBOL(read_cache_page_gfp);
+
+/*
+ * Warn about a page cache invalidation failure during a direct I/O write.
+ */
+static void dio_warn_stale_pagecache(struct file *filp)
+{
+	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
+	char pathname[128];
+	char *path;
+
+	errseq_set(&filp->f_mapping->wb_err, -EIO);
+	if (__ratelimit(&_rs)) {
+		path = file_path(filp, pathname, sizeof(pathname));
+		if (IS_ERR(path))
+			path = "(unknown)";
+		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
+		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
+			current->comm);
+	}
+}
+
+void kiocb_invalidate_post_direct_write(struct kiocb *iocb, size_t count)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+
+	if (mapping->nrpages &&
+	    invalidate_inode_pages2_range(mapping,
+			iocb->ki_pos >> PAGE_SHIFT,
+			(iocb->ki_pos + count - 1) >> PAGE_SHIFT))
+		dio_warn_stale_pagecache(iocb->ki_filp);
+}
+
+ssize_t
+generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	size_t write_len = iov_iter_count(from);
+	ssize_t written;
+
+	/*
+	 * If a page can not be invalidated, return 0 to fall back
+	 * to buffered write.
+	 */
+	written = kiocb_invalidate_pages(iocb, write_len);
+	if (written) {
+		if (written == -EBUSY)
+			return 0;
+		return written;
+	}
+
+	written = mapping->a_ops->direct_IO(iocb, from);
+
+	/*
+	 * Finally, try again to invalidate clean pages which might have been
+	 * cached by non-direct readahead, or faulted in by get_user_pages()
+	 * if the source of the write was an mmap'ed region of the file
+	 * we're writing.  Either one is a pretty crazy thing to do,
+	 * so we don't support it 100%.  If this invalidation
+	 * fails, tough, the write still worked...
+	 *
+	 * Most of the time we do not need this since dio_complete() will do
+	 * the invalidation for us. However there are some file systems that
+	 * do not end up with dio_complete() being called, so let's not break
+	 * them by removing it completely.
+	 *
+	 * Noticeable example is a blkdev_direct_IO().
+	 *
+	 * Skip invalidation for async writes or if mapping has no pages.
+	 */
+	if (written > 0) {
+		struct inode *inode = mapping->host;
+		loff_t pos = iocb->ki_pos;
+
+		kiocb_invalidate_post_direct_write(iocb, written);
+		pos += written;
+		write_len -= written;
+		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
+			i_size_write(inode, pos);
+			mark_inode_dirty(inode);
+		}
+		iocb->ki_pos = pos;
+	}
+	if (written != -EIOCBQUEUED)
+		iov_iter_revert(from, write_len - iov_iter_count(from));
+	return written;
+}
+EXPORT_SYMBOL(generic_file_direct_write);
+
+ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
+{
+	struct file *file = iocb->ki_filp;
+	loff_t pos = iocb->ki_pos;
+	struct address_space *mapping = file->f_mapping;
+	const struct address_space_operations *a_ops = mapping->a_ops;
+	long status = 0;
+	ssize_t written = 0;
+
+	do {
+		struct page *page;
+		unsigned long offset;	/* Offset into pagecache page */
+		unsigned long bytes;	/* Bytes to write to page */
+		size_t copied;		/* Bytes copied from user */
+		void *fsdata = NULL;
+
+		offset = (pos & (PAGE_SIZE - 1));
+		bytes = min_t(unsigned long, PAGE_SIZE - offset,
+						iov_iter_count(i));
+
+again:
+		/*
+		 * Bring in the user page that we will copy from _first_.
+		 * Otherwise there's a nasty deadlock on copying from the
+		 * same page as we're writing to, without it being marked
+		 * up-to-date.
+		 */
+		if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
+			status = -EFAULT;
+			break;
+		}
+
+		if (fatal_signal_pending(current)) {
+			status = -EINTR;
+			break;
+		}
+
+		status = a_ops->write_begin(file, mapping, pos, bytes,
+						&page, &fsdata);
+		if (unlikely(status < 0))
+			break;
+
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
+		copied = copy_page_from_iter_atomic(page, offset, bytes, i);
+		flush_dcache_page(page);
+
+		status = a_ops->write_end(file, mapping, pos, bytes, copied,
+						page, fsdata);
+		if (unlikely(status != copied)) {
+			iov_iter_revert(i, copied - max(status, 0L));
+			if (unlikely(status < 0))
+				break;
+		}
+		cond_resched();
+
+		if (unlikely(status == 0)) {
+			/*
+			 * A short copy made ->write_end() reject the
+			 * thing entirely.  Might be memory poisoning
+			 * halfway through, might be a race with munmap,
+			 * might be severe memory pressure.
+			 */
+			if (copied)
+				bytes = copied;
+			goto again;
+		}
+		pos += status;
+		written += status;
+
+		balance_dirty_pages_ratelimited(mapping);
+	} while (iov_iter_count(i));
+
+	if (!written)
+		return status;
+	iocb->ki_pos += written;
+	return written;
+}
+EXPORT_SYMBOL(generic_perform_write);
+
+/**
+ * __generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure (file, offset, etc.)
+ * @from:	iov_iter with data to write
+ *
+ * This function does all the work needed for actually writing data to a
+ * file. It does all basic checks, removes SUID from the file, updates
+ * modification times and calls proper subroutines depending on whether we
+ * do direct IO or a standard buffered write.
+ *
+ * It expects i_rwsem to be grabbed unless we work on a block device or similar
+ * object which does not need locking at all.
+ *
+ * This function does *not* take care of syncing data in case of O_SYNC write.
+ * A caller has to handle it. This is mainly due to the fact that we want to
+ * avoid syncing under i_rwsem.
+ *
+ * Return:
+ * * number of bytes written, even for truncated writes
+ * * negative error code if no data has been written at all
+ */
+ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	ssize_t ret;
+
+	ret = file_remove_privs(file);
+	if (ret)
+		return ret;
+
+	ret = file_update_time(file);
+	if (ret)
+		return ret;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		ret = generic_file_direct_write(iocb, from);
+		/*
+		 * If the write stopped short of completing, fall back to
+		 * buffered writes.  Some filesystems do this for writes to
+		 * holes, for example.  For DAX files, a buffered write will
+		 * not succeed (even if it did, DAX does not handle dirty
+		 * page-cache pages correctly).
+		 */
+		if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
+			return ret;
+		return direct_write_fallback(iocb, from, ret,
+				generic_perform_write(iocb, from));
+	}
+
+	return generic_perform_write(iocb, from);
+}
+EXPORT_SYMBOL(__generic_file_write_iter);
+
+/**
+ * generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure
+ * @from:	iov_iter with data to write
+ *
+ * This is a wrapper around __generic_file_write_iter() to be used by most
+ * filesystems. It takes care of syncing the file in case of O_SYNC file
+ * and acquires i_rwsem as needed.
+ * Return:
+ * * negative error code if no data has been written at all of
+ *   vfs_fsync_range() failed for a synchronous write
+ * * number of bytes written, even for truncated writes
+ */
+ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file->f_mapping->host;
+	ssize_t ret;
+
+	inode_lock(inode);
+	ret = generic_write_checks(iocb, from);
+	if (ret > 0)
+		ret = __generic_file_write_iter(iocb, from);
+	inode_unlock(inode);
+
+	if (ret > 0)
+		ret = generic_write_sync(iocb, ret);
+	return ret;
+}
+EXPORT_SYMBOL(generic_file_write_iter);
+
+/**
+ * filemap_release_folio() - Release fs-specific metadata on a folio.
+ * @folio: The folio which the kernel is trying to free.
+ * @gfp: Memory allocation flags (and I/O mode).
+ *
+ * The address_space is trying to release any data attached to a folio
+ * (presumably at folio->private).
+ *
+ * This will also be called if the private_2 flag is set on a page,
+ * indicating that the folio has other metadata associated with it.
+ *
+ * The @gfp argument specifies whether I/O may be performed to release
+ * this page (__GFP_IO), and whether the call may block
+ * (__GFP_RECLAIM & __GFP_FS).
+ *
+ * Return: %true if the release was successful, otherwise %false.
+ */
+bool filemap_release_folio(struct folio *folio, gfp_t gfp)
+{
+	struct address_space * const mapping = folio->mapping;
+
+	BUG_ON(!folio_test_locked(folio));
+	if (!folio_needs_release(folio))
+		return true;
+	if (folio_test_writeback(folio))
+		return false;
+
+	if (mapping && mapping->a_ops->release_folio)
+		return mapping->a_ops->release_folio(folio, gfp);
+	return try_to_free_buffers(folio);
+}
+EXPORT_SYMBOL(filemap_release_folio);
+
+#ifdef CONFIG_CACHESTAT_SYSCALL
+/**
+ * filemap_cachestat() - compute the page cache statistics of a mapping
+ * @mapping:	The mapping to compute the statistics for.
+ * @first_index:	The starting page cache index.
+ * @last_index:	The final page index (inclusive).
+ * @cs:	the cachestat struct to write the result to.
+ *
+ * This will query the page cache statistics of a mapping in the
+ * page range of [first_index, last_index] (inclusive). The statistics
+ * queried include: number of dirty pages, number of pages marked for
+ * writeback, and the number of (recently) evicted pages.
+ */
+static void filemap_cachestat(struct address_space *mapping,
+		pgoff_t first_index, pgoff_t last_index, struct cachestat *cs)
+{
+	XA_STATE(xas, &mapping->i_pages, first_index);
+	struct folio *folio;
+
+	rcu_read_lock();
+	xas_for_each(&xas, folio, last_index) {
+		unsigned long nr_pages;
+		pgoff_t folio_first_index, folio_last_index;
+
+		if (xas_retry(&xas, folio))
+			continue;
+
+		if (xa_is_value(folio)) {
+			/* page is evicted */
+			void *shadow = (void *)folio;
+			bool workingset; /* not used */
+			int order = xa_get_order(xas.xa, xas.xa_index);
+
+			nr_pages = 1 << order;
+			folio_first_index = round_down(xas.xa_index, 1 << order);
+			folio_last_index = folio_first_index + nr_pages - 1;
+
+			/* Folios might straddle the range boundaries, only count covered pages */
+			if (folio_first_index < first_index)
+				nr_pages -= first_index - folio_first_index;
+
+			if (folio_last_index > last_index)
+				nr_pages -= folio_last_index - last_index;
+
+			cs->nr_evicted += nr_pages;
+
+#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
+			if (shmem_mapping(mapping)) {
+				/* shmem file - in swap cache */
+				swp_entry_t swp = radix_to_swp_entry(folio);
+
+				shadow = get_shadow_from_swap_cache(swp);
+			}
+#endif
+			if (workingset_test_recent(shadow, true, &workingset))
+				cs->nr_recently_evicted += nr_pages;
+
+			goto resched;
+		}
+
+		nr_pages = folio_nr_pages(folio);
+		folio_first_index = folio_pgoff(folio);
+		folio_last_index = folio_first_index + nr_pages - 1;
+
+		/* Folios might straddle the range boundaries, only count covered pages */
+		if (folio_first_index < first_index)
+			nr_pages -= first_index - folio_first_index;
+
+		if (folio_last_index > last_index)
+			nr_pages -= folio_last_index - last_index;
+
+		/* page is in cache */
+		cs->nr_cache += nr_pages;
+
+		if (folio_test_dirty(folio))
+			cs->nr_dirty += nr_pages;
+
+		if (folio_test_writeback(folio))
+			cs->nr_writeback += nr_pages;
+
+resched:
+		if (need_resched()) {
+			xas_pause(&xas);
+			cond_resched_rcu();
+		}
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * The cachestat(2) system call.
+ *
+ * cachestat() returns the page cache statistics of a file in the
+ * bytes range specified by `off` and `len`: number of cached pages,
+ * number of dirty pages, number of pages marked for writeback,
+ * number of evicted pages, and number of recently evicted pages.
+ *
+ * An evicted page is a page that is previously in the page cache
+ * but has been evicted since. A page is recently evicted if its last
+ * eviction was recent enough that its reentry to the cache would
+ * indicate that it is actively being used by the system, and that
+ * there is memory pressure on the system.
+ *
+ * `off` and `len` must be non-negative integers. If `len` > 0,
+ * the queried range is [`off`, `off` + `len`]. If `len` == 0,
+ * we will query in the range from `off` to the end of the file.
+ *
+ * The `flags` argument is unused for now, but is included for future
+ * extensibility. User should pass 0 (i.e no flag specified).
+ *
+ * Currently, hugetlbfs is not supported.
+ *
+ * Because the status of a page can change after cachestat() checks it
+ * but before it returns to the application, the returned values may
+ * contain stale information.
+ *
+ * return values:
+ *  zero        - success
+ *  -EFAULT     - cstat or cstat_range points to an illegal address
+ *  -EINVAL     - invalid flags
+ *  -EBADF      - invalid file descriptor
+ *  -EOPNOTSUPP - file descriptor is of a hugetlbfs file
+ */
+SYSCALL_DEFINE4(cachestat, unsigned int, fd,
+		struct cachestat_range __user *, cstat_range,
+		struct cachestat __user *, cstat, unsigned int, flags)
+{
+	struct fd f = fdget(fd);
+	struct address_space *mapping;
+	struct cachestat_range csr;
+	struct cachestat cs;
+	pgoff_t first_index, last_index;
+
+	if (!f.file)
+		return -EBADF;
+
+	if (copy_from_user(&csr, cstat_range,
+			sizeof(struct cachestat_range))) {
+		fdput(f);
+		return -EFAULT;
+	}
+
+	/* hugetlbfs is not supported */
+	if (is_file_hugepages(f.file)) {
+		fdput(f);
+		return -EOPNOTSUPP;
+	}
+
+	if (flags != 0) {
+		fdput(f);
+		return -EINVAL;
+	}
+
+	first_index = csr.off >> PAGE_SHIFT;
+	last_index =
+		csr.len == 0 ? ULONG_MAX : (csr.off + csr.len - 1) >> PAGE_SHIFT;
+	memset(&cs, 0, sizeof(struct cachestat));
+	mapping = f.file->f_mapping;
+	filemap_cachestat(mapping, first_index, last_index, &cs);
+	fdput(f);
+
+	if (copy_to_user(cstat, &cs, sizeof(struct cachestat)))
+		return -EFAULT;
+
+	return 0;
+}
+#endif /* CONFIG_CACHESTAT_SYSCALL */