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-rw-r--r--mm/readahead.c1003
1 files changed, 622 insertions, 381 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index 829a77c62834..b415c9969176 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
/*
* mm/readahead.c - address_space-level file readahead.
*
@@ -7,18 +8,131 @@
* Initial version.
*/
+/**
+ * DOC: Readahead Overview
+ *
+ * Readahead is used to read content into the page cache before it is
+ * explicitly requested by the application. Readahead only ever
+ * attempts to read folios that are not yet in the page cache. If a
+ * folio is present but not up-to-date, readahead will not try to read
+ * it. In that case a simple ->read_folio() will be requested.
+ *
+ * Readahead is triggered when an application read request (whether a
+ * system call or a page fault) finds that the requested folio is not in
+ * the page cache, or that it is in the page cache and has the
+ * readahead flag set. This flag indicates that the folio was read
+ * as part of a previous readahead request and now that it has been
+ * accessed, it is time for the next readahead.
+ *
+ * Each readahead request is partly synchronous read, and partly async
+ * readahead. This is reflected in the struct file_ra_state which
+ * contains ->size being the total number of pages, and ->async_size
+ * which is the number of pages in the async section. The readahead
+ * flag will be set on the first folio in this async section to trigger
+ * a subsequent readahead. Once a series of sequential reads has been
+ * established, there should be no need for a synchronous component and
+ * all readahead request will be fully asynchronous.
+ *
+ * When either of the triggers causes a readahead, three numbers need
+ * to be determined: the start of the region to read, the size of the
+ * region, and the size of the async tail.
+ *
+ * The start of the region is simply the first page address at or after
+ * the accessed address, which is not currently populated in the page
+ * cache. This is found with a simple search in the page cache.
+ *
+ * The size of the async tail is determined by subtracting the size that
+ * was explicitly requested from the determined request size, unless
+ * this would be less than zero - then zero is used. NOTE THIS
+ * CALCULATION IS WRONG WHEN THE START OF THE REGION IS NOT THE ACCESSED
+ * PAGE. ALSO THIS CALCULATION IS NOT USED CONSISTENTLY.
+ *
+ * The size of the region is normally determined from the size of the
+ * previous readahead which loaded the preceding pages. This may be
+ * discovered from the struct file_ra_state for simple sequential reads,
+ * or from examining the state of the page cache when multiple
+ * sequential reads are interleaved. Specifically: where the readahead
+ * was triggered by the readahead flag, the size of the previous
+ * readahead is assumed to be the number of pages from the triggering
+ * page to the start of the new readahead. In these cases, the size of
+ * the previous readahead is scaled, often doubled, for the new
+ * readahead, though see get_next_ra_size() for details.
+ *
+ * If the size of the previous read cannot be determined, the number of
+ * preceding pages in the page cache is used to estimate the size of
+ * a previous read. This estimate could easily be misled by random
+ * reads being coincidentally adjacent, so it is ignored unless it is
+ * larger than the current request, and it is not scaled up, unless it
+ * is at the start of file.
+ *
+ * In general readahead is accelerated at the start of the file, as
+ * reads from there are often sequential. There are other minor
+ * adjustments to the readahead size in various special cases and these
+ * are best discovered by reading the code.
+ *
+ * The above calculation, based on the previous readahead size,
+ * determines the size of the readahead, to which any requested read
+ * size may be added.
+ *
+ * Readahead requests are sent to the filesystem using the ->readahead()
+ * address space operation, for which mpage_readahead() is a canonical
+ * implementation. ->readahead() should normally initiate reads on all
+ * folios, but may fail to read any or all folios without causing an I/O
+ * error. The page cache reading code will issue a ->read_folio() request
+ * for any folio which ->readahead() did not read, and only an error
+ * from this will be final.
+ *
+ * ->readahead() will generally call readahead_folio() repeatedly to get
+ * each folio from those prepared for readahead. It may fail to read a
+ * folio by:
+ *
+ * * not calling readahead_folio() sufficiently many times, effectively
+ * ignoring some folios, as might be appropriate if the path to
+ * storage is congested.
+ *
+ * * failing to actually submit a read request for a given folio,
+ * possibly due to insufficient resources, or
+ *
+ * * getting an error during subsequent processing of a request.
+ *
+ * In the last two cases, the folio should be unlocked by the filesystem
+ * to indicate that the read attempt has failed. In the first case the
+ * folio will be unlocked by the VFS.
+ *
+ * Those folios not in the final ``async_size`` of the request should be
+ * considered to be important and ->readahead() should not fail them due
+ * to congestion or temporary resource unavailability, but should wait
+ * for necessary resources (e.g. memory or indexing information) to
+ * become available. Folios in the final ``async_size`` may be
+ * considered less urgent and failure to read them is more acceptable.
+ * In this case it is best to use filemap_remove_folio() to remove the
+ * folios from the page cache as is automatically done for folios that
+ * were not fetched with readahead_folio(). This will allow a
+ * subsequent synchronous readahead request to try them again. If they
+ * are left in the page cache, then they will be read individually using
+ * ->read_folio() which may be less efficient.
+ */
+
+#include <linux/blkdev.h>
#include <linux/kernel.h>
-#include <linux/fs.h>
+#include <linux/dax.h>
#include <linux/gfp.h>
-#include <linux/mm.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/psi.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>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/readahead.h>
+
+#include "internal.h"
/*
* Initialise a struct file's readahead state. Assumes that the caller has
@@ -27,245 +141,234 @@
void
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
{
- ra->ra_pages = mapping->backing_dev_info->ra_pages;
+ ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
ra->prev_pos = -1;
}
EXPORT_SYMBOL_GPL(file_ra_state_init);
-#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
-
-/*
- * 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)
+static void read_pages(struct readahead_control *rac)
{
- if (page_has_private(page)) {
- if (!trylock_page(page))
- BUG();
- page->mapping = mapping;
- do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
- page->mapping = NULL;
- unlock_page(page);
+ const struct address_space_operations *aops = rac->mapping->a_ops;
+ struct folio *folio;
+ struct blk_plug plug;
+
+ if (!readahead_count(rac))
+ return;
+
+ if (unlikely(rac->_workingset))
+ psi_memstall_enter(&rac->_pflags);
+ blk_start_plug(&plug);
+
+ if (aops->readahead) {
+ aops->readahead(rac);
+ /* Clean up the remaining folios. */
+ while ((folio = readahead_folio(rac)) != NULL) {
+ folio_get(folio);
+ filemap_remove_folio(folio);
+ folio_unlock(folio);
+ folio_put(folio);
+ }
+ } else {
+ while ((folio = readahead_folio(rac)) != NULL)
+ aops->read_folio(rac->file, folio);
}
- page_cache_release(page);
+
+ blk_finish_plug(&plug);
+ if (unlikely(rac->_workingset))
+ psi_memstall_leave(&rac->_pflags);
+ rac->_workingset = false;
+
+ BUG_ON(readahead_count(rac));
}
-/*
- * 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)
+static struct folio *ractl_alloc_folio(struct readahead_control *ractl,
+ gfp_t gfp_mask, unsigned int order)
{
- struct page *victim;
+ struct folio *folio;
- while (!list_empty(pages)) {
- victim = list_to_page(pages);
- list_del(&victim->lru);
- read_cache_pages_invalidate_page(mapping, victim);
- }
+ folio = filemap_alloc_folio(gfp_mask, order, NULL);
+ if (folio && ractl->dropbehind)
+ __folio_set_dropbehind(folio);
+
+ return folio;
}
/**
- * 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.
+ * 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.
*
- * Hides the details of the LRU cache etc from the filesystems.
+ * 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.
*/
-int read_cache_pages(struct address_space *mapping, struct list_head *pages,
- int (*filler)(void *, struct page *), void *data)
+void page_cache_ra_unbounded(struct readahead_control *ractl,
+ unsigned long nr_to_read, unsigned long lookahead_size)
{
- struct page *page;
- int ret = 0;
-
- while (!list_empty(pages)) {
- page = list_to_page(pages);
- list_del(&page->lru);
- if (add_to_page_cache_lru(page, mapping,
- page->index, GFP_KERNEL)) {
- read_cache_pages_invalidate_page(mapping, page);
- continue;
- }
- page_cache_release(page);
+ struct address_space *mapping = ractl->mapping;
+ unsigned long index = readahead_index(ractl);
+ gfp_t gfp_mask = readahead_gfp_mask(mapping);
+ unsigned long mark = ULONG_MAX, i = 0;
+ unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
- ret = filler(data, page);
- if (unlikely(ret)) {
- read_cache_pages_invalidate_pages(mapping, pages);
- break;
- }
- task_io_account_read(PAGE_CACHE_SIZE);
- }
- return ret;
-}
-
-EXPORT_SYMBOL(read_cache_pages);
+ /*
+ * 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();
-static int read_pages(struct address_space *mapping, struct file *filp,
- struct list_head *pages, unsigned nr_pages)
-{
- struct blk_plug plug;
- unsigned page_idx;
- int ret;
+ trace_page_cache_ra_unbounded(mapping->host, index, nr_to_read,
+ lookahead_size);
+ filemap_invalidate_lock_shared(mapping);
+ index = mapping_align_index(mapping, index);
- blk_start_plug(&plug);
+ /*
+ * As iterator `i` is aligned to min_nrpages, round_up the
+ * difference between nr_to_read and lookahead_size to mark the
+ * index that only has lookahead or "async_region" to set the
+ * readahead flag.
+ */
+ if (lookahead_size <= nr_to_read) {
+ unsigned long ra_folio_index;
- if (mapping->a_ops->readpages) {
- ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
- /* Clean up the remaining pages */
- put_pages_list(pages);
- goto out;
+ ra_folio_index = round_up(readahead_index(ractl) +
+ nr_to_read - lookahead_size,
+ min_nrpages);
+ mark = ra_folio_index - index;
}
+ nr_to_read += readahead_index(ractl) - index;
+ ractl->_index = index;
+
+ /*
+ * Preallocate as many pages as we will need.
+ */
+ while (i < nr_to_read) {
+ struct folio *folio = xa_load(&mapping->i_pages, index + i);
+ int ret;
+
+ if (folio && !xa_is_value(folio)) {
+ /*
+ * 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);
+ ractl->_index += min_nrpages;
+ i = ractl->_index + ractl->_nr_pages - index;
+ continue;
+ }
- for (page_idx = 0; page_idx < nr_pages; page_idx++) {
- struct page *page = list_to_page(pages);
- list_del(&page->lru);
- if (!add_to_page_cache_lru(page, mapping,
- page->index, GFP_KERNEL)) {
- mapping->a_ops->readpage(filp, page);
+ folio = ractl_alloc_folio(ractl, gfp_mask,
+ mapping_min_folio_order(mapping));
+ if (!folio)
+ break;
+
+ ret = filemap_add_folio(mapping, folio, index + i, gfp_mask);
+ if (ret < 0) {
+ folio_put(folio);
+ if (ret == -ENOMEM)
+ break;
+ read_pages(ractl);
+ ractl->_index += min_nrpages;
+ i = ractl->_index + ractl->_nr_pages - index;
+ continue;
}
- page_cache_release(page);
+ if (i == mark)
+ folio_set_readahead(folio);
+ ractl->_workingset |= folio_test_workingset(folio);
+ ractl->_nr_pages += min_nrpages;
+ i += min_nrpages;
}
- ret = 0;
-out:
- blk_finish_plug(&plug);
-
- return ret;
+ /*
+ * Now start the IO. We ignore I/O errors - if the folio is not
+ * uptodate then the caller will launch read_folio again, and
+ * will then handle the error.
+ */
+ read_pages(ractl);
+ filemap_invalidate_unlock_shared(mapping);
+ memalloc_nofs_restore(nofs);
}
+EXPORT_SYMBOL_GPL(page_cache_ra_unbounded);
/*
- * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
- * the pages first, then submits them all for I/O. This avoids the very bad
+ * 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.
- *
- * Returns the number of pages requested, or the maximum amount of I/O allowed.
*/
-static int
-__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
- pgoff_t offset, unsigned long nr_to_read,
- unsigned long lookahead_size)
+static void do_page_cache_ra(struct readahead_control *ractl,
+ unsigned long nr_to_read, unsigned long lookahead_size)
{
- struct inode *inode = mapping->host;
- struct page *page;
- unsigned long end_index; /* The last page we want to read */
- LIST_HEAD(page_pool);
- int page_idx;
- int ret = 0;
+ 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)
- goto out;
-
- end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
-
- /*
- * Preallocate as many pages as we will need.
- */
- for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
- pgoff_t page_offset = offset + page_idx;
-
- if (page_offset > end_index)
- break;
-
- rcu_read_lock();
- page = radix_tree_lookup(&mapping->page_tree, page_offset);
- rcu_read_unlock();
- if (page)
- continue;
+ return;
- page = page_cache_alloc_readahead(mapping);
- if (!page)
- break;
- page->index = page_offset;
- list_add(&page->lru, &page_pool);
- if (page_idx == nr_to_read - lookahead_size)
- SetPageReadahead(page);
- ret++;
- }
+ 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;
- /*
- * 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.
- */
- if (ret)
- read_pages(mapping, filp, &page_pool, ret);
- BUG_ON(!list_empty(&page_pool));
-out:
- return ret;
+ 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.
*/
-int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
- pgoff_t offset, unsigned long nr_to_read)
+void force_page_cache_ra(struct readahead_control *ractl,
+ unsigned long nr_to_read)
{
- int ret = 0;
+ struct address_space *mapping = ractl->mapping;
+ struct file_ra_state *ra = ractl->ra;
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ unsigned long max_pages;
- if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
- return -EINVAL;
+ if (unlikely(!mapping->a_ops->read_folio && !mapping->a_ops->readahead))
+ return;
- nr_to_read = max_sane_readahead(nr_to_read);
+ /*
+ * If the request exceeds the readahead window, allow the read to
+ * be up to the optimal hardware IO size
+ */
+ 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) {
- int err;
-
- unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE;
+ unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
if (this_chunk > nr_to_read)
this_chunk = nr_to_read;
- err = __do_page_cache_readahead(mapping, filp,
- offset, this_chunk, 0);
- if (err < 0) {
- ret = err;
- break;
- }
- ret += err;
- offset += this_chunk;
+ do_page_cache_ra(ractl, this_chunk, 0);
+
nr_to_read -= this_chunk;
}
- return ret;
-}
-
-/*
- * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
- * sensible upper limit.
- */
-unsigned long max_sane_readahead(unsigned long nr)
-{
- return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
- + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
-}
-
-/*
- * Submit IO for the read-ahead request in file_ra_state.
- */
-unsigned long ra_submit(struct file_ra_state *ra,
- struct address_space *mapping, struct file *filp)
-{
- int actual;
-
- actual = __do_page_cache_readahead(mapping, filp,
- ra->start, ra->size, ra->async_size);
-
- return actual;
}
/*
* 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
+ * 1-2 page = 16k, 3-4 page 32k, 5-8 page = 64k, > 8 page = 128k initial
*/
static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
{
@@ -286,17 +389,15 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
* return it as the new window size.
*/
static unsigned long get_next_ra_size(struct file_ra_state *ra,
- unsigned long max)
+ unsigned long max)
{
unsigned long cur = ra->size;
- unsigned long newsize;
if (cur < max / 16)
- newsize = 4 * cur;
- else
- newsize = 2 * cur;
-
- return min(newsize, max);
+ return 4 * cur;
+ if (cur <= max / 2)
+ return 2 * cur;
+ return max;
}
/*
@@ -338,260 +439,400 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
* it approaches max_readhead.
*/
-/*
- * Count contiguously cached pages from @offset-1 to @offset-@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,
- struct file_ra_state *ra,
- pgoff_t offset, unsigned long max)
+static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index,
+ pgoff_t mark, unsigned int order, gfp_t gfp)
{
- pgoff_t head;
-
- rcu_read_lock();
- head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max);
- rcu_read_unlock();
+ int err;
+ struct folio *folio = ractl_alloc_folio(ractl, gfp, order);
+
+ if (!folio)
+ return -ENOMEM;
+ mark = round_down(mark, 1UL << order);
+ if (index == mark)
+ folio_set_readahead(folio);
+ err = filemap_add_folio(ractl->mapping, folio, index, gfp);
+ if (err) {
+ folio_put(folio);
+ return err;
+ }
- return offset - 1 - head;
+ ractl->_nr_pages += 1UL << order;
+ ractl->_workingset |= folio_test_workingset(folio);
+ return 0;
}
-/*
- * page cache context based read-ahead
- */
-static int try_context_readahead(struct address_space *mapping,
- struct file_ra_state *ra,
- pgoff_t offset,
- unsigned long req_size,
- unsigned long max)
+void page_cache_ra_order(struct readahead_control *ractl,
+ struct file_ra_state *ra)
{
- pgoff_t size;
+ struct address_space *mapping = ractl->mapping;
+ pgoff_t start = readahead_index(ractl);
+ pgoff_t index = start;
+ unsigned int min_order = mapping_min_folio_order(mapping);
+ pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
+ pgoff_t mark = index + ra->size - ra->async_size;
+ unsigned int nofs;
+ int err = 0;
+ gfp_t gfp = readahead_gfp_mask(mapping);
+ unsigned int new_order = ra->order;
+
+ trace_page_cache_ra_order(mapping->host, start, ra);
+ if (!mapping_large_folio_support(mapping)) {
+ ra->order = 0;
+ goto fallback;
+ }
+
+ limit = min(limit, index + ra->size - 1);
- size = count_history_pages(mapping, ra, offset, max);
+ new_order = min(mapping_max_folio_order(mapping), new_order);
+ new_order = min_t(unsigned int, new_order, ilog2(ra->size));
+ new_order = max(new_order, min_order);
+ ra->order = new_order;
+
+ /* See comment in page_cache_ra_unbounded() */
+ nofs = memalloc_nofs_save();
+ filemap_invalidate_lock_shared(mapping);
/*
- * no history pages:
- * it could be a random read
+ * If the new_order is greater than min_order and index is
+ * already aligned to new_order, then this will be noop as index
+ * aligned to new_order should also be aligned to min_order.
*/
- if (!size)
- return 0;
+ ractl->_index = mapping_align_index(mapping, index);
+ index = readahead_index(ractl);
+
+ while (index <= limit) {
+ unsigned int order = new_order;
+
+ /* Align with smaller pages if needed */
+ if (index & ((1UL << order) - 1))
+ order = __ffs(index);
+ /* Don't allocate pages past EOF */
+ while (order > min_order && index + (1UL << order) - 1 > limit)
+ order--;
+ err = ra_alloc_folio(ractl, index, mark, order, gfp);
+ if (err)
+ break;
+ index += 1UL << order;
+ }
+
+ read_pages(ractl);
+ filemap_invalidate_unlock_shared(mapping);
+ memalloc_nofs_restore(nofs);
/*
- * starts from beginning of file:
- * it is a strong indication of long-run stream (or whole-file-read)
+ * If there were already pages in the page cache, then we may have
+ * left some gaps. Let the regular readahead code take care of this
+ * situation below.
+ */
+ if (!err)
+ return;
+fallback:
+ /*
+ * ->readahead() may have updated readahead window size so we have to
+ * check there's still something to read.
*/
- if (size >= offset)
- size *= 2;
+ if (ra->size > index - start)
+ do_page_cache_ra(ractl, ra->size - (index - start),
+ ra->async_size);
+}
- ra->start = offset;
- ra->size = get_init_ra_size(size + req_size, max);
- ra->async_size = ra->size;
+static unsigned long ractl_max_pages(struct readahead_control *ractl,
+ unsigned long req_size)
+{
+ struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
+ unsigned long max_pages = ractl->ra->ra_pages;
- return 1;
+ /*
+ * 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);
+ return max_pages;
}
-/*
- * A minimal readahead algorithm for trivial sequential/random reads.
- */
-static unsigned long
-ondemand_readahead(struct address_space *mapping,
- struct file_ra_state *ra, struct file *filp,
- bool hit_readahead_marker, pgoff_t offset,
- unsigned long req_size)
+void page_cache_sync_ra(struct readahead_control *ractl,
+ unsigned long req_count)
{
- unsigned long max = max_sane_readahead(ra->ra_pages);
+ pgoff_t index = readahead_index(ractl);
+ bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
+ struct file_ra_state *ra = ractl->ra;
+ unsigned long max_pages, contig_count;
+ pgoff_t prev_index, miss;
+ trace_page_cache_sync_ra(ractl->mapping->host, index, ra, req_count);
/*
- * start of file
+ * Even if readahead is disabled, issue this request as readahead
+ * as we'll need it to satisfy the requested range. The forced
+ * readahead 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 (!offset)
- goto initial_readahead;
+ 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, req_count);
+ return;
+ }
+ max_pages = ractl_max_pages(ractl, req_count);
+ prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
/*
- * It's the expected callback offset, assume sequential access.
- * Ramp up sizes, and push forward the readahead window.
+ * A start of file, oversized read, or sequential cache miss:
+ * trivial case: (index - prev_index) == 1
+ * unaligned reads: (index - prev_index) == 0
*/
- if ((offset == (ra->start + ra->size - ra->async_size) ||
- offset == (ra->start + ra->size))) {
- ra->start += ra->size;
- ra->size = get_next_ra_size(ra, max);
- ra->async_size = ra->size;
+ if (!index || req_count > max_pages || index - prev_index <= 1UL) {
+ ra->start = index;
+ ra->size = get_init_ra_size(req_count, max_pages);
+ ra->async_size = ra->size > req_count ? ra->size - req_count :
+ ra->size >> 1;
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.
+ * Query the page cache and look for the traces(cached history pages)
+ * that a sequential stream would leave behind.
*/
- if (hit_readahead_marker) {
- pgoff_t start;
-
- rcu_read_lock();
- start = radix_tree_next_hole(&mapping->page_tree, offset+1,max);
- rcu_read_unlock();
-
- if (!start || start - offset > max)
- return 0;
-
- ra->start = start;
- ra->size = start - offset; /* old async_size */
- ra->size += req_size;
- ra->size = get_next_ra_size(ra, max);
- ra->async_size = ra->size;
- goto readit;
+ rcu_read_lock();
+ miss = page_cache_prev_miss(ractl->mapping, index - 1, max_pages);
+ rcu_read_unlock();
+ contig_count = index - miss - 1;
+ /*
+ * Standalone, small random read. Read as is, and do not pollute the
+ * readahead state.
+ */
+ if (contig_count <= req_count) {
+ do_page_cache_ra(ractl, req_count, 0);
+ return;
}
-
/*
- * oversize read
+ * File cached from the beginning:
+ * it is a strong indication of long-run stream (or whole-file-read)
*/
- if (req_size > max)
- goto initial_readahead;
+ if (miss == ULONG_MAX)
+ contig_count *= 2;
+ ra->start = index;
+ ra->size = min(contig_count + req_count, max_pages);
+ ra->async_size = 1;
+readit:
+ ra->order = 0;
+ ractl->_index = ra->start;
+ page_cache_ra_order(ractl, ra);
+}
+EXPORT_SYMBOL_GPL(page_cache_sync_ra);
+
+void page_cache_async_ra(struct readahead_control *ractl,
+ struct folio *folio, unsigned long req_count)
+{
+ unsigned long max_pages;
+ struct file_ra_state *ra = ractl->ra;
+ pgoff_t index = readahead_index(ractl);
+ pgoff_t expected, start, end, aligned_end, align;
+
+ /* no readahead */
+ if (!ra->ra_pages)
+ return;
/*
- * sequential cache miss
+ * Same bit is used for PG_readahead and PG_reclaim.
*/
- if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL)
- goto initial_readahead;
+ if (folio_test_writeback(folio))
+ return;
+ trace_page_cache_async_ra(ractl->mapping->host, index, ra, req_count);
+ folio_clear_readahead(folio);
+
+ if (blk_cgroup_congested())
+ return;
+
+ max_pages = ractl_max_pages(ractl, req_count);
/*
- * Query the page cache and look for the traces(cached history pages)
- * that a sequential stream would leave behind.
+ * It's the expected callback index, assume sequential access.
+ * Ramp up sizes, and push forward the readahead window.
*/
- if (try_context_readahead(mapping, ra, offset, req_size, max))
+ expected = round_down(ra->start + ra->size - ra->async_size,
+ folio_nr_pages(folio));
+ if (index == expected) {
+ ra->start += ra->size;
+ /*
+ * In the case of MADV_HUGEPAGE, the actual size might exceed
+ * the readahead window.
+ */
+ ra->size = max(ra->size, get_next_ra_size(ra, max_pages));
goto readit;
+ }
/*
- * standalone, small random read
- * Read as is, and do not pollute the readahead state.
+ * Hit a marked folio 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.
*/
- return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
+ rcu_read_lock();
+ start = page_cache_next_miss(ractl->mapping, index + 1, max_pages);
+ rcu_read_unlock();
-initial_readahead:
- ra->start = offset;
- ra->size = get_init_ra_size(req_size, max);
- ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
+ if (!start || start - index > max_pages)
+ return;
+ ra->start = start;
+ ra->size = start - index; /* old async_size */
+ ra->size += req_count;
+ ra->size = get_next_ra_size(ra, max_pages);
readit:
+ ra->order += 2;
+ align = 1UL << min(ra->order, ffs(max_pages) - 1);
+ end = ra->start + ra->size;
+ aligned_end = round_down(end, align);
+ if (aligned_end > ra->start)
+ ra->size -= end - aligned_end;
+ ra->async_size = ra->size;
+ ractl->_index = ra->start;
+ page_cache_ra_order(ractl, ra);
+}
+EXPORT_SYMBOL_GPL(page_cache_async_ra);
+
+ssize_t ksys_readahead(int fd, loff_t offset, size_t count)
+{
+ struct file *file;
+ const struct inode *inode;
+
+ CLASS(fd, f)(fd);
+ if (fd_empty(f))
+ return -EBADF;
+
+ file = fd_file(f);
+ if (!(file->f_mode & FMODE_READ))
+ return -EBADF;
+
/*
- * 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.
+ * 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.
*/
- if (offset == ra->start && ra->size == ra->async_size) {
- ra->async_size = get_next_ra_size(ra, max);
- ra->size += ra->async_size;
- }
+ if (!file->f_mapping)
+ return -EINVAL;
+ if (!file->f_mapping->a_ops)
+ return -EINVAL;
- return ra_submit(ra, mapping, filp);
+ inode = file_inode(file);
+ if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
+ return -EINVAL;
+ if (IS_ANON_FILE(inode))
+ return -EINVAL;
+
+ return vfs_fadvise(fd_file(f), offset, count, POSIX_FADV_WILLNEED);
}
-/**
- * page_cache_sync_readahead - generic file readahead
- * @mapping: address_space which holds the pagecache and I/O vectors
- * @ra: file_ra_state which holds the readahead state
- * @filp: passed on to ->readpage() and ->readpages()
- * @offset: start offset into @mapping, in pagecache page-sized units
- * @req_size: hint: total size of the read which the caller is performing in
- * pagecache pages
- *
- * page_cache_sync_readahead() should be called when a cache miss happened:
- * it will submit the read. The readahead logic may decide to piggyback more
- * pages onto the read request if access patterns suggest it will improve
- * performance.
- */
-void page_cache_sync_readahead(struct address_space *mapping,
- struct file_ra_state *ra, struct file *filp,
- pgoff_t offset, unsigned long req_size)
+SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
{
- /* no read-ahead */
- if (!ra->ra_pages)
- return;
-
- /* be dumb */
- if (filp && (filp->f_mode & FMODE_RANDOM)) {
- force_page_cache_readahead(mapping, filp, offset, req_size);
- return;
- }
+ return ksys_readahead(fd, offset, count);
+}
- /* do read-ahead */
- ondemand_readahead(mapping, ra, filp, false, offset, req_size);
+#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_READAHEAD)
+COMPAT_SYSCALL_DEFINE4(readahead, int, fd, compat_arg_u64_dual(offset), size_t, count)
+{
+ return ksys_readahead(fd, compat_arg_u64_glue(offset), count);
}
-EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
+#endif
/**
- * page_cache_async_readahead - file readahead for marked pages
- * @mapping: address_space which holds the pagecache and I/O vectors
- * @ra: file_ra_state which holds the readahead state
- * @filp: passed on to ->readpage() and ->readpages()
- * @page: the page at @offset which has the PG_readahead flag set
- * @offset: start offset into @mapping, in pagecache page-sized units
- * @req_size: hint: total size of the read which the caller is performing in
- * pagecache pages
+ * readahead_expand - Expand a readahead request
+ * @ractl: The request to be expanded
+ * @new_start: The revised start
+ * @new_len: The revised size of the request
+ *
+ * Attempt to expand a readahead request outwards from the current size to the
+ * specified size by inserting locked pages before and after the current window
+ * to increase the size to the new window. This may involve the insertion of
+ * THPs, in which case the window may get expanded even beyond what was
+ * requested.
*
- * page_cache_async_readahead() should be called when a page is used which
- * has the PG_readahead flag; this is a marker to suggest that the application
- * has used up enough of the readahead window that we should start pulling in
- * more pages.
+ * The algorithm will stop if it encounters a conflicting page already in the
+ * pagecache and leave a smaller expansion than requested.
+ *
+ * The caller must check for this by examining the revised @ractl object for a
+ * different expansion than was requested.
*/
-void
-page_cache_async_readahead(struct address_space *mapping,
- struct file_ra_state *ra, struct file *filp,
- struct page *page, pgoff_t offset,
- unsigned long req_size)
+void readahead_expand(struct readahead_control *ractl,
+ loff_t new_start, size_t new_len)
{
- /* no read-ahead */
- if (!ra->ra_pages)
- return;
-
+ struct address_space *mapping = ractl->mapping;
+ struct file_ra_state *ra = ractl->ra;
+ pgoff_t new_index, new_nr_pages;
+ gfp_t gfp_mask = readahead_gfp_mask(mapping);
+ unsigned long min_nrpages = mapping_min_folio_nrpages(mapping);
+ unsigned int min_order = mapping_min_folio_order(mapping);
+
+ new_index = new_start / PAGE_SIZE;
/*
- * Same bit is used for PG_readahead and PG_reclaim.
+ * Readahead code should have aligned the ractl->_index to
+ * min_nrpages before calling readahead aops.
*/
- if (PageWriteback(page))
- return;
+ VM_BUG_ON(!IS_ALIGNED(ractl->_index, min_nrpages));
- ClearPageReadahead(page);
+ /* Expand the leading edge downwards */
+ while (ractl->_index > new_index) {
+ unsigned long index = ractl->_index - 1;
+ struct folio *folio = xa_load(&mapping->i_pages, index);
- /*
- * Defer asynchronous read-ahead on IO congestion.
- */
- if (bdi_read_congested(mapping->backing_dev_info))
- return;
+ if (folio && !xa_is_value(folio))
+ return; /* Folio apparently present */
- /* do read-ahead */
- ondemand_readahead(mapping, ra, filp, true, offset, req_size);
-}
-EXPORT_SYMBOL_GPL(page_cache_async_readahead);
+ folio = ractl_alloc_folio(ractl, gfp_mask, min_order);
+ if (!folio)
+ return;
-static ssize_t
-do_readahead(struct address_space *mapping, struct file *filp,
- pgoff_t index, unsigned long nr)
-{
- if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
- return -EINVAL;
+ index = mapping_align_index(mapping, index);
+ if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) {
+ folio_put(folio);
+ return;
+ }
+ if (unlikely(folio_test_workingset(folio)) &&
+ !ractl->_workingset) {
+ ractl->_workingset = true;
+ psi_memstall_enter(&ractl->_pflags);
+ }
+ ractl->_nr_pages += min_nrpages;
+ ractl->_index = folio->index;
+ }
- force_page_cache_readahead(mapping, filp, index, nr);
- return 0;
-}
+ new_len += new_start - readahead_pos(ractl);
+ new_nr_pages = DIV_ROUND_UP(new_len, PAGE_SIZE);
-SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
-{
- ssize_t ret;
- struct fd f;
-
- ret = -EBADF;
- f = fdget(fd);
- if (f.file) {
- if (f.file->f_mode & FMODE_READ) {
- struct address_space *mapping = f.file->f_mapping;
- pgoff_t start = offset >> PAGE_CACHE_SHIFT;
- pgoff_t end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
- unsigned long len = end - start + 1;
- ret = do_readahead(mapping, f.file, start, len);
+ /* Expand the trailing edge upwards */
+ while (ractl->_nr_pages < new_nr_pages) {
+ unsigned long index = ractl->_index + ractl->_nr_pages;
+ struct folio *folio = xa_load(&mapping->i_pages, index);
+
+ if (folio && !xa_is_value(folio))
+ return; /* Folio apparently present */
+
+ folio = ractl_alloc_folio(ractl, gfp_mask, min_order);
+ if (!folio)
+ return;
+
+ index = mapping_align_index(mapping, index);
+ if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) {
+ folio_put(folio);
+ return;
+ }
+ if (unlikely(folio_test_workingset(folio)) &&
+ !ractl->_workingset) {
+ ractl->_workingset = true;
+ psi_memstall_enter(&ractl->_pflags);
+ }
+ ractl->_nr_pages += min_nrpages;
+ if (ra) {
+ ra->size += min_nrpages;
+ ra->async_size += min_nrpages;
}
- fdput(f);
}
- return ret;
}
+EXPORT_SYMBOL(readahead_expand);
generated by cgit (git 2.34.1) at 2025-12-21 21:35:16 +0000