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-rw-r--r--mm/readahead.c641
1 files changed, 641 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
new file mode 100644
index 000000000..d30bcf4bc
--- /dev/null
+++ b/mm/readahead.c
@@ -0,0 +1,641 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * mm/readahead.c - address_space-level file readahead.
+ *
+ * Copyright (C) 2002, Linus Torvalds
+ *
+ * 09Apr2002 Andrew Morton
+ * Initial version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/dax.h>
+#include <linux/gfp.h>
+#include <linux/export.h>
+#include <linux/blkdev.h>
+#include <linux/backing-dev.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/pagevec.h>
+#include <linux/pagemap.h>
+#include <linux/syscalls.h>
+#include <linux/file.h>
+#include <linux/mm_inline.h>
+#include <linux/blk-cgroup.h>
+#include <linux/fadvise.h>
+#include <linux/sched/mm.h>
+
+#include "internal.h"
+
+/*
+ * Initialise a struct file's readahead state. Assumes that the caller has
+ * memset *ra to zero.
+ */
+void
+file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
+{
+ ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
+ ra->prev_pos = -1;
+}
+EXPORT_SYMBOL_GPL(file_ra_state_init);
+
+/*
+ * see if a page needs releasing upon read_cache_pages() failure
+ * - the caller of read_cache_pages() may have set PG_private or PG_fscache
+ * before calling, such as the NFS fs marking pages that are cached locally
+ * on disk, thus we need to give the fs a chance to clean up in the event of
+ * an error
+ */
+static void read_cache_pages_invalidate_page(struct address_space *mapping,
+ struct page *page)
+{
+ if (page_has_private(page)) {
+ if (!trylock_page(page))
+ BUG();
+ page->mapping = mapping;
+ do_invalidatepage(page, 0, PAGE_SIZE);
+ page->mapping = NULL;
+ unlock_page(page);
+ }
+ put_page(page);
+}
+
+/*
+ * release a list of pages, invalidating them first if need be
+ */
+static void read_cache_pages_invalidate_pages(struct address_space *mapping,
+ struct list_head *pages)
+{
+ struct page *victim;
+
+ while (!list_empty(pages)) {
+ victim = lru_to_page(pages);
+ list_del(&victim->lru);
+ read_cache_pages_invalidate_page(mapping, victim);
+ }
+}
+
+/**
+ * read_cache_pages - populate an address space with some pages & start reads against them
+ * @mapping: the address_space
+ * @pages: The address of a list_head which contains the target pages. These
+ * pages have their ->index populated and are otherwise uninitialised.
+ * @filler: callback routine for filling a single page.
+ * @data: private data for the callback routine.
+ *
+ * Hides the details of the LRU cache etc from the filesystems.
+ *
+ * Returns: %0 on success, error return by @filler otherwise
+ */
+int read_cache_pages(struct address_space *mapping, struct list_head *pages,
+ int (*filler)(void *, struct page *), void *data)
+{
+ struct page *page;
+ int ret = 0;
+
+ while (!list_empty(pages)) {
+ page = lru_to_page(pages);
+ list_del(&page->lru);
+ if (add_to_page_cache_lru(page, mapping, page->index,
+ readahead_gfp_mask(mapping))) {
+ read_cache_pages_invalidate_page(mapping, page);
+ continue;
+ }
+ put_page(page);
+
+ ret = filler(data, page);
+ if (unlikely(ret)) {
+ read_cache_pages_invalidate_pages(mapping, pages);
+ break;
+ }
+ task_io_account_read(PAGE_SIZE);
+ }
+ return ret;
+}
+
+EXPORT_SYMBOL(read_cache_pages);
+
+static void read_pages(struct readahead_control *rac, struct list_head *pages,
+ bool skip_page)
+{
+ const struct address_space_operations *aops = rac->mapping->a_ops;
+ struct page *page;
+ struct blk_plug plug;
+
+ if (!readahead_count(rac))
+ goto out;
+
+ blk_start_plug(&plug);
+
+ if (aops->readahead) {
+ aops->readahead(rac);
+ /* Clean up the remaining pages */
+ while ((page = readahead_page(rac))) {
+ unlock_page(page);
+ put_page(page);
+ }
+ } else if (aops->readpages) {
+ aops->readpages(rac->file, rac->mapping, pages,
+ readahead_count(rac));
+ /* Clean up the remaining pages */
+ put_pages_list(pages);
+ rac->_index += rac->_nr_pages;
+ rac->_nr_pages = 0;
+ } else {
+ while ((page = readahead_page(rac))) {
+ aops->readpage(rac->file, page);
+ put_page(page);
+ }
+ }
+
+ blk_finish_plug(&plug);
+
+ BUG_ON(!list_empty(pages));
+ BUG_ON(readahead_count(rac));
+
+out:
+ if (skip_page)
+ rac->_index++;
+}
+
+/**
+ * page_cache_ra_unbounded - Start unchecked readahead.
+ * @ractl: Readahead control.
+ * @nr_to_read: The number of pages to read.
+ * @lookahead_size: Where to start the next readahead.
+ *
+ * This function is for filesystems to call when they want to start
+ * readahead beyond a file's stated i_size. This is almost certainly
+ * not the function you want to call. Use page_cache_async_readahead()
+ * or page_cache_sync_readahead() instead.
+ *
+ * Context: File is referenced by caller. Mutexes may be held by caller.
+ * May sleep, but will not reenter filesystem to reclaim memory.
+ */
+void page_cache_ra_unbounded(struct readahead_control *ractl,
+ unsigned long nr_to_read, unsigned long lookahead_size)
+{
+ struct address_space *mapping = ractl->mapping;
+ unsigned long index = readahead_index(ractl);
+ LIST_HEAD(page_pool);
+ gfp_t gfp_mask = readahead_gfp_mask(mapping);
+ unsigned long i;
+
+ /*
+ * Partway through the readahead operation, we will have added
+ * locked pages to the page cache, but will not yet have submitted
+ * them for I/O. Adding another page may need to allocate memory,
+ * which can trigger memory reclaim. Telling the VM we're in
+ * the middle of a filesystem operation will cause it to not
+ * touch file-backed pages, preventing a deadlock. Most (all?)
+ * filesystems already specify __GFP_NOFS in their mapping's
+ * gfp_mask, but let's be explicit here.
+ */
+ unsigned int nofs = memalloc_nofs_save();
+
+ /*
+ * Preallocate as many pages as we will need.
+ */
+ for (i = 0; i < nr_to_read; i++) {
+ struct page *page = xa_load(&mapping->i_pages, index + i);
+
+ BUG_ON(index + i != ractl->_index + ractl->_nr_pages);
+
+ if (page && !xa_is_value(page)) {
+ /*
+ * Page already present? Kick off the current batch
+ * of contiguous pages before continuing with the
+ * next batch. This page may be the one we would
+ * have intended to mark as Readahead, but we don't
+ * have a stable reference to this page, and it's
+ * not worth getting one just for that.
+ */
+ read_pages(ractl, &page_pool, true);
+ continue;
+ }
+
+ page = __page_cache_alloc(gfp_mask);
+ if (!page)
+ break;
+ if (mapping->a_ops->readpages) {
+ page->index = index + i;
+ list_add(&page->lru, &page_pool);
+ } else if (add_to_page_cache_lru(page, mapping, index + i,
+ gfp_mask) < 0) {
+ put_page(page);
+ read_pages(ractl, &page_pool, true);
+ continue;
+ }
+ if (i == nr_to_read - lookahead_size)
+ SetPageReadahead(page);
+ ractl->_nr_pages++;
+ }
+
+ /*
+ * Now start the IO. We ignore I/O errors - if the page is not
+ * uptodate then the caller will launch readpage again, and
+ * will then handle the error.
+ */
+ read_pages(ractl, &page_pool, false);
+ memalloc_nofs_restore(nofs);
+}
+EXPORT_SYMBOL_GPL(page_cache_ra_unbounded);
+
+/*
+ * do_page_cache_ra() actually reads a chunk of disk. It allocates
+ * the pages first, then submits them for I/O. This avoids the very bad
+ * behaviour which would occur if page allocations are causing VM writeback.
+ * We really don't want to intermingle reads and writes like that.
+ */
+void do_page_cache_ra(struct readahead_control *ractl,
+ unsigned long nr_to_read, unsigned long lookahead_size)
+{
+ struct inode *inode = ractl->mapping->host;
+ unsigned long index = readahead_index(ractl);
+ loff_t isize = i_size_read(inode);
+ pgoff_t end_index; /* The last page we want to read */
+
+ if (isize == 0)
+ return;
+
+ end_index = (isize - 1) >> PAGE_SHIFT;
+ if (index > end_index)
+ return;
+ /* Don't read past the page containing the last byte of the file */
+ if (nr_to_read > end_index - index)
+ nr_to_read = end_index - index + 1;
+
+ page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size);
+}
+
+/*
+ * Chunk the readahead into 2 megabyte units, so that we don't pin too much
+ * memory at once.
+ */
+void force_page_cache_ra(struct readahead_control *ractl,
+ struct file_ra_state *ra, unsigned long nr_to_read)
+{
+ struct address_space *mapping = ractl->mapping;
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ unsigned long max_pages, index;
+
+ if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
+ !mapping->a_ops->readahead))
+ return;
+
+ /*
+ * If the request exceeds the readahead window, allow the read to
+ * be up to the optimal hardware IO size
+ */
+ index = readahead_index(ractl);
+ max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
+ nr_to_read = min_t(unsigned long, nr_to_read, max_pages);
+ while (nr_to_read) {
+ unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
+
+ if (this_chunk > nr_to_read)
+ this_chunk = nr_to_read;
+ ractl->_index = index;
+ do_page_cache_ra(ractl, this_chunk, 0);
+
+ index += this_chunk;
+ nr_to_read -= this_chunk;
+ }
+}
+
+/*
+ * Set the initial window size, round to next power of 2 and square
+ * for small size, x 4 for medium, and x 2 for large
+ * for 128k (32 page) max ra
+ * 1-8 page = 32k initial, > 8 page = 128k initial
+ */
+static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
+{
+ unsigned long newsize = roundup_pow_of_two(size);
+
+ if (newsize <= max / 32)
+ newsize = newsize * 4;
+ else if (newsize <= max / 4)
+ newsize = newsize * 2;
+ else
+ newsize = max;
+
+ return newsize;
+}
+
+/*
+ * Get the previous window size, ramp it up, and
+ * return it as the new window size.
+ */
+static unsigned long get_next_ra_size(struct file_ra_state *ra,
+ unsigned long max)
+{
+ unsigned long cur = ra->size;
+
+ if (cur < max / 16)
+ return 4 * cur;
+ if (cur <= max / 2)
+ return 2 * cur;
+ return max;
+}
+
+/*
+ * On-demand readahead design.
+ *
+ * The fields in struct file_ra_state represent the most-recently-executed
+ * readahead attempt:
+ *
+ * |<----- async_size ---------|
+ * |------------------- size -------------------->|
+ * |==================#===========================|
+ * ^start ^page marked with PG_readahead
+ *
+ * To overlap application thinking time and disk I/O time, we do
+ * `readahead pipelining': Do not wait until the application consumed all
+ * readahead pages and stalled on the missing page at readahead_index;
+ * Instead, submit an asynchronous readahead I/O as soon as there are
+ * only async_size pages left in the readahead window. Normally async_size
+ * will be equal to size, for maximum pipelining.
+ *
+ * In interleaved sequential reads, concurrent streams on the same fd can
+ * be invalidating each other's readahead state. So we flag the new readahead
+ * page at (start+size-async_size) with PG_readahead, and use it as readahead
+ * indicator. The flag won't be set on already cached pages, to avoid the
+ * readahead-for-nothing fuss, saving pointless page cache lookups.
+ *
+ * prev_pos tracks the last visited byte in the _previous_ read request.
+ * It should be maintained by the caller, and will be used for detecting
+ * small random reads. Note that the readahead algorithm checks loosely
+ * for sequential patterns. Hence interleaved reads might be served as
+ * sequential ones.
+ *
+ * There is a special-case: if the first page which the application tries to
+ * read happens to be the first page of the file, it is assumed that a linear
+ * read is about to happen and the window is immediately set to the initial size
+ * based on I/O request size and the max_readahead.
+ *
+ * The code ramps up the readahead size aggressively at first, but slow down as
+ * it approaches max_readhead.
+ */
+
+/*
+ * Count contiguously cached pages from @index-1 to @index-@max,
+ * this count is a conservative estimation of
+ * - length of the sequential read sequence, or
+ * - thrashing threshold in memory tight systems
+ */
+static pgoff_t count_history_pages(struct address_space *mapping,
+ pgoff_t index, unsigned long max)
+{
+ pgoff_t head;
+
+ rcu_read_lock();
+ head = page_cache_prev_miss(mapping, index - 1, max);
+ rcu_read_unlock();
+
+ return index - 1 - head;
+}
+
+/*
+ * page cache context based read-ahead
+ */
+static int try_context_readahead(struct address_space *mapping,
+ struct file_ra_state *ra,
+ pgoff_t index,
+ unsigned long req_size,
+ unsigned long max)
+{
+ pgoff_t size;
+
+ size = count_history_pages(mapping, index, max);
+
+ /*
+ * not enough history pages:
+ * it could be a random read
+ */
+ if (size <= req_size)
+ return 0;
+
+ /*
+ * starts from beginning of file:
+ * it is a strong indication of long-run stream (or whole-file-read)
+ */
+ if (size >= index)
+ size *= 2;
+
+ ra->start = index;
+ ra->size = min(size + req_size, max);
+ ra->async_size = 1;
+
+ return 1;
+}
+
+/*
+ * A minimal readahead algorithm for trivial sequential/random reads.
+ */
+static void ondemand_readahead(struct readahead_control *ractl,
+ struct file_ra_state *ra, bool hit_readahead_marker,
+ unsigned long req_size)
+{
+ struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
+ unsigned long max_pages = ra->ra_pages;
+ unsigned long add_pages;
+ unsigned long index = readahead_index(ractl);
+ pgoff_t prev_index;
+
+ /*
+ * If the request exceeds the readahead window, allow the read to
+ * be up to the optimal hardware IO size
+ */
+ if (req_size > max_pages && bdi->io_pages > max_pages)
+ max_pages = min(req_size, bdi->io_pages);
+
+ /*
+ * start of file
+ */
+ if (!index)
+ goto initial_readahead;
+
+ /*
+ * It's the expected callback index, assume sequential access.
+ * Ramp up sizes, and push forward the readahead window.
+ */
+ if ((index == (ra->start + ra->size - ra->async_size) ||
+ index == (ra->start + ra->size))) {
+ ra->start += ra->size;
+ ra->size = get_next_ra_size(ra, max_pages);
+ ra->async_size = ra->size;
+ goto readit;
+ }
+
+ /*
+ * Hit a marked page without valid readahead state.
+ * E.g. interleaved reads.
+ * Query the pagecache for async_size, which normally equals to
+ * readahead size. Ramp it up and use it as the new readahead size.
+ */
+ if (hit_readahead_marker) {
+ pgoff_t start;
+
+ rcu_read_lock();
+ start = page_cache_next_miss(ractl->mapping, index + 1,
+ max_pages);
+ rcu_read_unlock();
+
+ if (!start || start - index > max_pages)
+ return;
+
+ ra->start = start;
+ ra->size = start - index; /* old async_size */
+ ra->size += req_size;
+ ra->size = get_next_ra_size(ra, max_pages);
+ ra->async_size = ra->size;
+ goto readit;
+ }
+
+ /*
+ * oversize read
+ */
+ if (req_size > max_pages)
+ goto initial_readahead;
+
+ /*
+ * sequential cache miss
+ * trivial case: (index - prev_index) == 1
+ * unaligned reads: (index - prev_index) == 0
+ */
+ prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
+ if (index - prev_index <= 1UL)
+ goto initial_readahead;
+
+ /*
+ * Query the page cache and look for the traces(cached history pages)
+ * that a sequential stream would leave behind.
+ */
+ if (try_context_readahead(ractl->mapping, ra, index, req_size,
+ max_pages))
+ goto readit;
+
+ /*
+ * standalone, small random read
+ * Read as is, and do not pollute the readahead state.
+ */
+ do_page_cache_ra(ractl, req_size, 0);
+ return;
+
+initial_readahead:
+ ra->start = index;
+ ra->size = get_init_ra_size(req_size, max_pages);
+ ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
+
+readit:
+ /*
+ * Will this read hit the readahead marker made by itself?
+ * If so, trigger the readahead marker hit now, and merge
+ * the resulted next readahead window into the current one.
+ * Take care of maximum IO pages as above.
+ */
+ if (index == ra->start && ra->size == ra->async_size) {
+ add_pages = get_next_ra_size(ra, max_pages);
+ if (ra->size + add_pages <= max_pages) {
+ ra->async_size = add_pages;
+ ra->size += add_pages;
+ } else {
+ ra->size = max_pages;
+ ra->async_size = max_pages >> 1;
+ }
+ }
+
+ ractl->_index = ra->start;
+ do_page_cache_ra(ractl, ra->size, ra->async_size);
+}
+
+void page_cache_sync_ra(struct readahead_control *ractl,
+ struct file_ra_state *ra, unsigned long req_count)
+{
+ bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
+
+ /*
+ * Even if read-ahead is disabled, issue this request as read-ahead
+ * as we'll need it to satisfy the requested range. The forced
+ * read-ahead will do the right thing and limit the read to just the
+ * requested range, which we'll set to 1 page for this case.
+ */
+ if (!ra->ra_pages || blk_cgroup_congested()) {
+ if (!ractl->file)
+ return;
+ req_count = 1;
+ do_forced_ra = true;
+ }
+
+ /* be dumb */
+ if (do_forced_ra) {
+ force_page_cache_ra(ractl, ra, req_count);
+ return;
+ }
+
+ /* do read-ahead */
+ ondemand_readahead(ractl, ra, false, req_count);
+}
+EXPORT_SYMBOL_GPL(page_cache_sync_ra);
+
+void page_cache_async_ra(struct readahead_control *ractl,
+ struct file_ra_state *ra, struct page *page,
+ unsigned long req_count)
+{
+ /* no read-ahead */
+ if (!ra->ra_pages)
+ return;
+
+ /*
+ * Same bit is used for PG_readahead and PG_reclaim.
+ */
+ if (PageWriteback(page))
+ return;
+
+ ClearPageReadahead(page);
+
+ /*
+ * Defer asynchronous read-ahead on IO congestion.
+ */
+ if (inode_read_congested(ractl->mapping->host))
+ return;
+
+ if (blk_cgroup_congested())
+ return;
+
+ /* do read-ahead */
+ ondemand_readahead(ractl, ra, true, req_count);
+}
+EXPORT_SYMBOL_GPL(page_cache_async_ra);
+
+ssize_t ksys_readahead(int fd, loff_t offset, size_t count)
+{
+ ssize_t ret;
+ struct fd f;
+
+ ret = -EBADF;
+ f = fdget(fd);
+ if (!f.file || !(f.file->f_mode & FMODE_READ))
+ goto out;
+
+ /*
+ * The readahead() syscall is intended to run only on files
+ * that can execute readahead. If readahead is not possible
+ * on this file, then we must return -EINVAL.
+ */
+ ret = -EINVAL;
+ if (!f.file->f_mapping || !f.file->f_mapping->a_ops ||
+ (!S_ISREG(file_inode(f.file)->i_mode) &&
+ !S_ISBLK(file_inode(f.file)->i_mode)))
+ goto out;
+
+ ret = vfs_fadvise(f.file, offset, count, POSIX_FADV_WILLNEED);
+out:
+ fdput(f);
+ return ret;
+}
+
+SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
+{
+ return ksys_readahead(fd, offset, count);
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-22 16:51:16 +0000