Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 913 insertions, 0 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
new file mode 100644
index 0000000000..b3b14bd0dd
--- /dev/null
+++ b/mm/swap_state.c
@@ -0,0 +1,913 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/mm/swap_state.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *  Swap reorganised 29.12.95, Stephen Tweedie
+ *
+ *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
+ */
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/init.h>
+#include <linux/pagemap.h>
+#include <linux/backing-dev.h>
+#include <linux/blkdev.h>
+#include <linux/migrate.h>
+#include <linux/vmalloc.h>
+#include <linux/swap_slots.h>
+#include <linux/huge_mm.h>
+#include <linux/shmem_fs.h>
+#include "internal.h"
+#include "swap.h"
+
+/*
+ * swapper_space is a fiction, retained to simplify the path through
+ * vmscan's shrink_page_list.
+ */
+static const struct address_space_operations swap_aops = {
+	.writepage	= swap_writepage,
+	.dirty_folio	= noop_dirty_folio,
+#ifdef CONFIG_MIGRATION
+	.migrate_folio	= migrate_folio,
+#endif
+};
+
+struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
+static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
+static bool enable_vma_readahead __read_mostly = true;
+
+#define SWAP_RA_WIN_SHIFT	(PAGE_SHIFT / 2)
+#define SWAP_RA_HITS_MASK	((1UL << SWAP_RA_WIN_SHIFT) - 1)
+#define SWAP_RA_HITS_MAX	SWAP_RA_HITS_MASK
+#define SWAP_RA_WIN_MASK	(~PAGE_MASK & ~SWAP_RA_HITS_MASK)
+
+#define SWAP_RA_HITS(v)		((v) & SWAP_RA_HITS_MASK)
+#define SWAP_RA_WIN(v)		(((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
+#define SWAP_RA_ADDR(v)		((v) & PAGE_MASK)
+
+#define SWAP_RA_VAL(addr, win, hits)				\
+	(((addr) & PAGE_MASK) |					\
+	 (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |	\
+	 ((hits) & SWAP_RA_HITS_MASK))
+
+/* Initial readahead hits is 4 to start up with a small window */
+#define GET_SWAP_RA_VAL(vma)					\
+	(atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
+
+static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
+
+void show_swap_cache_info(void)
+{
+	printk("%lu pages in swap cache\n", total_swapcache_pages());
+	printk("Free swap  = %ldkB\n", K(get_nr_swap_pages()));
+	printk("Total swap = %lukB\n", K(total_swap_pages));
+}
+
+void *get_shadow_from_swap_cache(swp_entry_t entry)
+{
+	struct address_space *address_space = swap_address_space(entry);
+	pgoff_t idx = swp_offset(entry);
+	struct page *page;
+
+	page = xa_load(&address_space->i_pages, idx);
+	if (xa_is_value(page))
+		return page;
+	return NULL;
+}
+
+/*
+ * add_to_swap_cache resembles filemap_add_folio on swapper_space,
+ * but sets SwapCache flag and private instead of mapping and index.
+ */
+int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
+			gfp_t gfp, void **shadowp)
+{
+	struct address_space *address_space = swap_address_space(entry);
+	pgoff_t idx = swp_offset(entry);
+	XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio));
+	unsigned long i, nr = folio_nr_pages(folio);
+	void *old;
+
+	xas_set_update(&xas, workingset_update_node);
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
+	VM_BUG_ON_FOLIO(!folio_test_swapbacked(folio), folio);
+
+	folio_ref_add(folio, nr);
+	folio_set_swapcache(folio);
+	folio->swap = entry;
+
+	do {
+		xas_lock_irq(&xas);
+		xas_create_range(&xas);
+		if (xas_error(&xas))
+			goto unlock;
+		for (i = 0; i < nr; i++) {
+			VM_BUG_ON_FOLIO(xas.xa_index != idx + i, folio);
+			old = xas_load(&xas);
+			if (xa_is_value(old)) {
+				if (shadowp)
+					*shadowp = old;
+			}
+			xas_store(&xas, folio);
+			xas_next(&xas);
+		}
+		address_space->nrpages += nr;
+		__node_stat_mod_folio(folio, NR_FILE_PAGES, nr);
+		__lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr);
+unlock:
+		xas_unlock_irq(&xas);
+	} while (xas_nomem(&xas, gfp));
+
+	if (!xas_error(&xas))
+		return 0;
+
+	folio_clear_swapcache(folio);
+	folio_ref_sub(folio, nr);
+	return xas_error(&xas);
+}
+
+/*
+ * This must be called only on folios that have
+ * been verified to be in the swap cache.
+ */
+void __delete_from_swap_cache(struct folio *folio,
+			swp_entry_t entry, void *shadow)
+{
+	struct address_space *address_space = swap_address_space(entry);
+	int i;
+	long nr = folio_nr_pages(folio);
+	pgoff_t idx = swp_offset(entry);
+	XA_STATE(xas, &address_space->i_pages, idx);
+
+	xas_set_update(&xas, workingset_update_node);
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
+	VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
+
+	for (i = 0; i < nr; i++) {
+		void *entry = xas_store(&xas, shadow);
+		VM_BUG_ON_PAGE(entry != folio, entry);
+		xas_next(&xas);
+	}
+	folio->swap.val = 0;
+	folio_clear_swapcache(folio);
+	address_space->nrpages -= nr;
+	__node_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
+	__lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr);
+}
+
+/**
+ * add_to_swap - allocate swap space for a folio
+ * @folio: folio we want to move to swap
+ *
+ * Allocate swap space for the folio and add the folio to the
+ * swap cache.
+ *
+ * Context: Caller needs to hold the folio lock.
+ * Return: Whether the folio was added to the swap cache.
+ */
+bool add_to_swap(struct folio *folio)
+{
+	swp_entry_t entry;
+	int err;
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
+
+	entry = folio_alloc_swap(folio);
+	if (!entry.val)
+		return false;
+
+	/*
+	 * XArray node allocations from PF_MEMALLOC contexts could
+	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
+	 * stops emergency reserves from being allocated.
+	 *
+	 * TODO: this could cause a theoretical memory reclaim
+	 * deadlock in the swap out path.
+	 */
+	/*
+	 * Add it to the swap cache.
+	 */
+	err = add_to_swap_cache(folio, entry,
+			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
+	if (err)
+		/*
+		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+		 * clear SWAP_HAS_CACHE flag.
+		 */
+		goto fail;
+	/*
+	 * Normally the folio will be dirtied in unmap because its
+	 * pte should be dirty. A special case is MADV_FREE page. The
+	 * page's pte could have dirty bit cleared but the folio's
+	 * SwapBacked flag is still set because clearing the dirty bit
+	 * and SwapBacked flag has no lock protected. For such folio,
+	 * unmap will not set dirty bit for it, so folio reclaim will
+	 * not write the folio out. This can cause data corruption when
+	 * the folio is swapped in later. Always setting the dirty flag
+	 * for the folio solves the problem.
+	 */
+	folio_mark_dirty(folio);
+
+	return true;
+
+fail:
+	put_swap_folio(folio, entry);
+	return false;
+}
+
+/*
+ * This must be called only on folios that have
+ * been verified to be in the swap cache and locked.
+ * It will never put the folio into the free list,
+ * the caller has a reference on the folio.
+ */
+void delete_from_swap_cache(struct folio *folio)
+{
+	swp_entry_t entry = folio->swap;
+	struct address_space *address_space = swap_address_space(entry);
+
+	xa_lock_irq(&address_space->i_pages);
+	__delete_from_swap_cache(folio, entry, NULL);
+	xa_unlock_irq(&address_space->i_pages);
+
+	put_swap_folio(folio, entry);
+	folio_ref_sub(folio, folio_nr_pages(folio));
+}
+
+void clear_shadow_from_swap_cache(int type, unsigned long begin,
+				unsigned long end)
+{
+	unsigned long curr = begin;
+	void *old;
+
+	for (;;) {
+		swp_entry_t entry = swp_entry(type, curr);
+		struct address_space *address_space = swap_address_space(entry);
+		XA_STATE(xas, &address_space->i_pages, curr);
+
+		xas_set_update(&xas, workingset_update_node);
+
+		xa_lock_irq(&address_space->i_pages);
+		xas_for_each(&xas, old, end) {
+			if (!xa_is_value(old))
+				continue;
+			xas_store(&xas, NULL);
+		}
+		xa_unlock_irq(&address_space->i_pages);
+
+		/* search the next swapcache until we meet end */
+		curr >>= SWAP_ADDRESS_SPACE_SHIFT;
+		curr++;
+		curr <<= SWAP_ADDRESS_SPACE_SHIFT;
+		if (curr > end)
+			break;
+	}
+}
+
+/*
+ * If we are the only user, then try to free up the swap cache.
+ *
+ * Its ok to check the swapcache flag without the folio lock
+ * here because we are going to recheck again inside
+ * folio_free_swap() _with_ the lock.
+ * 					- Marcelo
+ */
+void free_swap_cache(struct page *page)
+{
+	struct folio *folio = page_folio(page);
+
+	if (folio_test_swapcache(folio) && !folio_mapped(folio) &&
+	    folio_trylock(folio)) {
+		folio_free_swap(folio);
+		folio_unlock(folio);
+	}
+}
+
+/*
+ * Perform a free_page(), also freeing any swap cache associated with
+ * this page if it is the last user of the page.
+ */
+void free_page_and_swap_cache(struct page *page)
+{
+	free_swap_cache(page);
+	if (!is_huge_zero_page(page))
+		put_page(page);
+}
+
+/*
+ * Passed an array of pages, drop them all from swapcache and then release
+ * them.  They are removed from the LRU and freed if this is their last use.
+ */
+void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
+{
+	lru_add_drain();
+	for (int i = 0; i < nr; i++)
+		free_swap_cache(encoded_page_ptr(pages[i]));
+	release_pages(pages, nr);
+}
+
+static inline bool swap_use_vma_readahead(void)
+{
+	return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
+}
+
+/*
+ * Lookup a swap entry in the swap cache. A found folio will be returned
+ * unlocked and with its refcount incremented - we rely on the kernel
+ * lock getting page table operations atomic even if we drop the folio
+ * lock before returning.
+ *
+ * Caller must lock the swap device or hold a reference to keep it valid.
+ */
+struct folio *swap_cache_get_folio(swp_entry_t entry,
+		struct vm_area_struct *vma, unsigned long addr)
+{
+	struct folio *folio;
+
+	folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry));
+	if (!IS_ERR(folio)) {
+		bool vma_ra = swap_use_vma_readahead();
+		bool readahead;
+
+		/*
+		 * At the moment, we don't support PG_readahead for anon THP
+		 * so let's bail out rather than confusing the readahead stat.
+		 */
+		if (unlikely(folio_test_large(folio)))
+			return folio;
+
+		readahead = folio_test_clear_readahead(folio);
+		if (vma && vma_ra) {
+			unsigned long ra_val;
+			int win, hits;
+
+			ra_val = GET_SWAP_RA_VAL(vma);
+			win = SWAP_RA_WIN(ra_val);
+			hits = SWAP_RA_HITS(ra_val);
+			if (readahead)
+				hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
+			atomic_long_set(&vma->swap_readahead_info,
+					SWAP_RA_VAL(addr, win, hits));
+		}
+
+		if (readahead) {
+			count_vm_event(SWAP_RA_HIT);
+			if (!vma || !vma_ra)
+				atomic_inc(&swapin_readahead_hits);
+		}
+	} else {
+		folio = NULL;
+	}
+
+	return folio;
+}
+
+/**
+ * filemap_get_incore_folio - Find and get a folio from the page or swap caches.
+ * @mapping: The address_space to search.
+ * @index: The page cache index.
+ *
+ * This differs from filemap_get_folio() in that it will also look for the
+ * folio in the swap cache.
+ *
+ * Return: The found folio or %NULL.
+ */
+struct folio *filemap_get_incore_folio(struct address_space *mapping,
+		pgoff_t index)
+{
+	swp_entry_t swp;
+	struct swap_info_struct *si;
+	struct folio *folio = filemap_get_entry(mapping, index);
+
+	if (!folio)
+		return ERR_PTR(-ENOENT);
+	if (!xa_is_value(folio))
+		return folio;
+	if (!shmem_mapping(mapping))
+		return ERR_PTR(-ENOENT);
+
+	swp = radix_to_swp_entry(folio);
+	/* There might be swapin error entries in shmem mapping. */
+	if (non_swap_entry(swp))
+		return ERR_PTR(-ENOENT);
+	/* Prevent swapoff from happening to us */
+	si = get_swap_device(swp);
+	if (!si)
+		return ERR_PTR(-ENOENT);
+	index = swp_offset(swp);
+	folio = filemap_get_folio(swap_address_space(swp), index);
+	put_swap_device(si);
+	return folio;
+}
+
+struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
+			struct vm_area_struct *vma, unsigned long addr,
+			bool *new_page_allocated)
+{
+	struct swap_info_struct *si;
+	struct folio *folio;
+	struct page *page;
+	void *shadow = NULL;
+
+	*new_page_allocated = false;
+	si = get_swap_device(entry);
+	if (!si)
+		return NULL;
+
+	for (;;) {
+		int err;
+		/*
+		 * First check the swap cache.  Since this is normally
+		 * called after swap_cache_get_folio() failed, re-calling
+		 * that would confuse statistics.
+		 */
+		folio = filemap_get_folio(swap_address_space(entry),
+						swp_offset(entry));
+		if (!IS_ERR(folio)) {
+			page = folio_file_page(folio, swp_offset(entry));
+			goto got_page;
+		}
+
+		/*
+		 * Just skip read ahead for unused swap slot.
+		 * During swap_off when swap_slot_cache is disabled,
+		 * we have to handle the race between putting
+		 * swap entry in swap cache and marking swap slot
+		 * as SWAP_HAS_CACHE.  That's done in later part of code or
+		 * else swap_off will be aborted if we return NULL.
+		 */
+		if (!swap_swapcount(si, entry) && swap_slot_cache_enabled)
+			goto fail_put_swap;
+
+		/*
+		 * Get a new page to read into from swap.  Allocate it now,
+		 * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
+		 * cause any racers to loop around until we add it to cache.
+		 */
+		folio = vma_alloc_folio(gfp_mask, 0, vma, addr, false);
+		if (!folio)
+                        goto fail_put_swap;
+
+		/*
+		 * Swap entry may have been freed since our caller observed it.
+		 */
+		err = swapcache_prepare(entry);
+		if (!err)
+			break;
+
+		folio_put(folio);
+		if (err != -EEXIST)
+			goto fail_put_swap;
+
+		/*
+		 * We might race against __delete_from_swap_cache(), and
+		 * stumble across a swap_map entry whose SWAP_HAS_CACHE
+		 * has not yet been cleared.  Or race against another
+		 * __read_swap_cache_async(), which has set SWAP_HAS_CACHE
+		 * in swap_map, but not yet added its page to swap cache.
+		 */
+		schedule_timeout_uninterruptible(1);
+	}
+
+	/*
+	 * The swap entry is ours to swap in. Prepare the new page.
+	 */
+
+	__folio_set_locked(folio);
+	__folio_set_swapbacked(folio);
+
+	if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry))
+		goto fail_unlock;
+
+	/* May fail (-ENOMEM) if XArray node allocation failed. */
+	if (add_to_swap_cache(folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
+		goto fail_unlock;
+
+	mem_cgroup_swapin_uncharge_swap(entry);
+
+	if (shadow)
+		workingset_refault(folio, shadow);
+
+	/* Caller will initiate read into locked folio */
+	folio_add_lru(folio);
+	*new_page_allocated = true;
+	page = &folio->page;
+got_page:
+	put_swap_device(si);
+	return page;
+
+fail_unlock:
+	put_swap_folio(folio, entry);
+	folio_unlock(folio);
+	folio_put(folio);
+fail_put_swap:
+	put_swap_device(si);
+	return NULL;
+}
+
+/*
+ * Locate a page of swap in physical memory, reserving swap cache space
+ * and reading the disk if it is not already cached.
+ * A failure return means that either the page allocation failed or that
+ * the swap entry is no longer in use.
+ *
+ * get/put_swap_device() aren't needed to call this function, because
+ * __read_swap_cache_async() call them and swap_readpage() holds the
+ * swap cache folio lock.
+ */
+struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
+				   struct vm_area_struct *vma,
+				   unsigned long addr, struct swap_iocb **plug)
+{
+	bool page_was_allocated;
+	struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
+			vma, addr, &page_was_allocated);
+
+	if (page_was_allocated)
+		swap_readpage(retpage, false, plug);
+
+	return retpage;
+}
+
+static unsigned int __swapin_nr_pages(unsigned long prev_offset,
+				      unsigned long offset,
+				      int hits,
+				      int max_pages,
+				      int prev_win)
+{
+	unsigned int pages, last_ra;
+
+	/*
+	 * This heuristic has been found to work well on both sequential and
+	 * random loads, swapping to hard disk or to SSD: please don't ask
+	 * what the "+ 2" means, it just happens to work well, that's all.
+	 */
+	pages = hits + 2;
+	if (pages == 2) {
+		/*
+		 * We can have no readahead hits to judge by: but must not get
+		 * stuck here forever, so check for an adjacent offset instead
+		 * (and don't even bother to check whether swap type is same).
+		 */
+		if (offset != prev_offset + 1 && offset != prev_offset - 1)
+			pages = 1;
+	} else {
+		unsigned int roundup = 4;
+		while (roundup < pages)
+			roundup <<= 1;
+		pages = roundup;
+	}
+
+	if (pages > max_pages)
+		pages = max_pages;
+
+	/* Don't shrink readahead too fast */
+	last_ra = prev_win / 2;
+	if (pages < last_ra)
+		pages = last_ra;
+
+	return pages;
+}
+
+static unsigned long swapin_nr_pages(unsigned long offset)
+{
+	static unsigned long prev_offset;
+	unsigned int hits, pages, max_pages;
+	static atomic_t last_readahead_pages;
+
+	max_pages = 1 << READ_ONCE(page_cluster);
+	if (max_pages <= 1)
+		return 1;
+
+	hits = atomic_xchg(&swapin_readahead_hits, 0);
+	pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
+				  max_pages,
+				  atomic_read(&last_readahead_pages));
+	if (!hits)
+		WRITE_ONCE(prev_offset, offset);
+	atomic_set(&last_readahead_pages, pages);
+
+	return pages;
+}
+
+/**
+ * swap_cluster_readahead - swap in pages in hope we need them soon
+ * @entry: swap entry of this memory
+ * @gfp_mask: memory allocation flags
+ * @vmf: fault information
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * Primitive swap readahead code. We simply read an aligned block of
+ * (1 << page_cluster) entries in the swap area. This method is chosen
+ * because it doesn't cost us any seek time.  We also make sure to queue
+ * the 'original' request together with the readahead ones...
+ *
+ * This has been extended to use the NUMA policies from the mm triggering
+ * the readahead.
+ *
+ * Caller must hold read mmap_lock if vmf->vma is not NULL.
+ */
+struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
+				struct vm_fault *vmf)
+{
+	struct page *page;
+	unsigned long entry_offset = swp_offset(entry);
+	unsigned long offset = entry_offset;
+	unsigned long start_offset, end_offset;
+	unsigned long mask;
+	struct swap_info_struct *si = swp_swap_info(entry);
+	struct blk_plug plug;
+	struct swap_iocb *splug = NULL;
+	bool page_allocated;
+	struct vm_area_struct *vma = vmf->vma;
+	unsigned long addr = vmf->address;
+
+	mask = swapin_nr_pages(offset) - 1;
+	if (!mask)
+		goto skip;
+
+	/* Read a page_cluster sized and aligned cluster around offset. */
+	start_offset = offset & ~mask;
+	end_offset = offset | mask;
+	if (!start_offset)	/* First page is swap header. */
+		start_offset++;
+	if (end_offset >= si->max)
+		end_offset = si->max - 1;
+
+	blk_start_plug(&plug);
+	for (offset = start_offset; offset <= end_offset ; offset++) {
+		/* Ok, do the async read-ahead now */
+		page = __read_swap_cache_async(
+			swp_entry(swp_type(entry), offset),
+			gfp_mask, vma, addr, &page_allocated);
+		if (!page)
+			continue;
+		if (page_allocated) {
+			swap_readpage(page, false, &splug);
+			if (offset != entry_offset) {
+				SetPageReadahead(page);
+				count_vm_event(SWAP_RA);
+			}
+		}
+		put_page(page);
+	}
+	blk_finish_plug(&plug);
+	swap_read_unplug(splug);
+
+	lru_add_drain();	/* Push any new pages onto the LRU now */
+skip:
+	/* The page was likely read above, so no need for plugging here */
+	return read_swap_cache_async(entry, gfp_mask, vma, addr, NULL);
+}
+
+int init_swap_address_space(unsigned int type, unsigned long nr_pages)
+{
+	struct address_space *spaces, *space;
+	unsigned int i, nr;
+
+	nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
+	spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
+	if (!spaces)
+		return -ENOMEM;
+	for (i = 0; i < nr; i++) {
+		space = spaces + i;
+		xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
+		atomic_set(&space->i_mmap_writable, 0);
+		space->a_ops = &swap_aops;
+		/* swap cache doesn't use writeback related tags */
+		mapping_set_no_writeback_tags(space);
+	}
+	nr_swapper_spaces[type] = nr;
+	swapper_spaces[type] = spaces;
+
+	return 0;
+}
+
+void exit_swap_address_space(unsigned int type)
+{
+	int i;
+	struct address_space *spaces = swapper_spaces[type];
+
+	for (i = 0; i < nr_swapper_spaces[type]; i++)
+		VM_WARN_ON_ONCE(!mapping_empty(&spaces[i]));
+	kvfree(spaces);
+	nr_swapper_spaces[type] = 0;
+	swapper_spaces[type] = NULL;
+}
+
+#define SWAP_RA_ORDER_CEILING	5
+
+struct vma_swap_readahead {
+	unsigned short win;
+	unsigned short offset;
+	unsigned short nr_pte;
+};
+
+static void swap_ra_info(struct vm_fault *vmf,
+			 struct vma_swap_readahead *ra_info)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	unsigned long ra_val;
+	unsigned long faddr, pfn, fpfn, lpfn, rpfn;
+	unsigned long start, end;
+	unsigned int max_win, hits, prev_win, win;
+
+	max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
+			     SWAP_RA_ORDER_CEILING);
+	if (max_win == 1) {
+		ra_info->win = 1;
+		return;
+	}
+
+	faddr = vmf->address;
+	fpfn = PFN_DOWN(faddr);
+	ra_val = GET_SWAP_RA_VAL(vma);
+	pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
+	prev_win = SWAP_RA_WIN(ra_val);
+	hits = SWAP_RA_HITS(ra_val);
+	ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
+					       max_win, prev_win);
+	atomic_long_set(&vma->swap_readahead_info,
+			SWAP_RA_VAL(faddr, win, 0));
+	if (win == 1)
+		return;
+
+	if (fpfn == pfn + 1) {
+		lpfn = fpfn;
+		rpfn = fpfn + win;
+	} else if (pfn == fpfn + 1) {
+		lpfn = fpfn - win + 1;
+		rpfn = fpfn + 1;
+	} else {
+		unsigned int left = (win - 1) / 2;
+
+		lpfn = fpfn - left;
+		rpfn = fpfn + win - left;
+	}
+	start = max3(lpfn, PFN_DOWN(vma->vm_start),
+		     PFN_DOWN(faddr & PMD_MASK));
+	end = min3(rpfn, PFN_DOWN(vma->vm_end),
+		   PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
+
+	ra_info->nr_pte = end - start;
+	ra_info->offset = fpfn - start;
+}
+
+/**
+ * swap_vma_readahead - swap in pages in hope we need them soon
+ * @fentry: swap entry of this memory
+ * @gfp_mask: memory allocation flags
+ * @vmf: fault information
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * Primitive swap readahead code. We simply read in a few pages whose
+ * virtual addresses are around the fault address in the same vma.
+ *
+ * Caller must hold read mmap_lock if vmf->vma is not NULL.
+ *
+ */
+static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
+				       struct vm_fault *vmf)
+{
+	struct blk_plug plug;
+	struct swap_iocb *splug = NULL;
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page;
+	pte_t *pte = NULL, pentry;
+	unsigned long addr;
+	swp_entry_t entry;
+	unsigned int i;
+	bool page_allocated;
+	struct vma_swap_readahead ra_info = {
+		.win = 1,
+	};
+
+	swap_ra_info(vmf, &ra_info);
+	if (ra_info.win == 1)
+		goto skip;
+
+	addr = vmf->address - (ra_info.offset * PAGE_SIZE);
+
+	blk_start_plug(&plug);
+	for (i = 0; i < ra_info.nr_pte; i++, addr += PAGE_SIZE) {
+		if (!pte++) {
+			pte = pte_offset_map(vmf->pmd, addr);
+			if (!pte)
+				break;
+		}
+		pentry = ptep_get_lockless(pte);
+		if (!is_swap_pte(pentry))
+			continue;
+		entry = pte_to_swp_entry(pentry);
+		if (unlikely(non_swap_entry(entry)))
+			continue;
+		pte_unmap(pte);
+		pte = NULL;
+		page = __read_swap_cache_async(entry, gfp_mask, vma,
+					       addr, &page_allocated);
+		if (!page)
+			continue;
+		if (page_allocated) {
+			swap_readpage(page, false, &splug);
+			if (i != ra_info.offset) {
+				SetPageReadahead(page);
+				count_vm_event(SWAP_RA);
+			}
+		}
+		put_page(page);
+	}
+	if (pte)
+		pte_unmap(pte);
+	blk_finish_plug(&plug);
+	swap_read_unplug(splug);
+	lru_add_drain();
+skip:
+	/* The page was likely read above, so no need for plugging here */
+	return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
+				     NULL);
+}
+
+/**
+ * swapin_readahead - swap in pages in hope we need them soon
+ * @entry: swap entry of this memory
+ * @gfp_mask: memory allocation flags
+ * @vmf: fault information
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * It's a main entry function for swap readahead. By the configuration,
+ * it will read ahead blocks by cluster-based(ie, physical disk based)
+ * or vma-based(ie, virtual address based on faulty address) readahead.
+ */
+struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
+				struct vm_fault *vmf)
+{
+	return swap_use_vma_readahead() ?
+			swap_vma_readahead(entry, gfp_mask, vmf) :
+			swap_cluster_readahead(entry, gfp_mask, vmf);
+}
+
+#ifdef CONFIG_SYSFS
+static ssize_t vma_ra_enabled_show(struct kobject *kobj,
+				     struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+			  enable_vma_readahead ? "true" : "false");
+}
+static ssize_t vma_ra_enabled_store(struct kobject *kobj,
+				      struct kobj_attribute *attr,
+				      const char *buf, size_t count)
+{
+	ssize_t ret;
+
+	ret = kstrtobool(buf, &enable_vma_readahead);
+	if (ret)
+		return ret;
+
+	return count;
+}
+static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled);
+
+static struct attribute *swap_attrs[] = {
+	&vma_ra_enabled_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group swap_attr_group = {
+	.attrs = swap_attrs,
+};
+
+static int __init swap_init_sysfs(void)
+{
+	int err;
+	struct kobject *swap_kobj;
+
+	swap_kobj = kobject_create_and_add("swap", mm_kobj);
+	if (!swap_kobj) {
+		pr_err("failed to create swap kobject\n");
+		return -ENOMEM;
+	}
+	err = sysfs_create_group(swap_kobj, &swap_attr_group);
+	if (err) {
+		pr_err("failed to register swap group\n");
+		goto delete_obj;
+	}
+	return 0;
+
+delete_obj:
+	kobject_put(swap_kobj);
+	return err;
+}
+subsys_initcall(swap_init_sysfs);
+#endif