Patch series "mm, netfs, fscache: Stop read optimisation when folio
removed from pagecache", v7.
This fixes an optimisation in fscache whereby we don't read from the cache
for a particular file until we know that there's data there that we don't
have in the pagecache. The problem is that I'm no longer using PG_fscache
(aka PG_private_2) to indicate that the page is cached and so I don't get
a notification when a cached page is dropped from the pagecache.
The first patch merges some folio_has_private() and
filemap_release_folio() pairs and introduces a helper,
folio_needs_release(), to indicate if a release is required.
The second patch is the actual fix. Following Willy's suggestions[1], it
adds an AS_RELEASE_ALWAYS flag to an address_space that will make
filemap_release_folio() always call ->release_folio(), even if
PG_private/PG_private_2 aren't set. folio_needs_release() is altered to
add a check for this.
This patch (of 2):
Make filemap_release_folio() check folio_has_private(). Then, in most
cases, where a call to folio_has_private() is immediately followed by a
call to filemap_release_folio(), we can get rid of the test in the pair.
There are a couple of sites in mm/vscan.c that this can't so easily be
done. In shrink_folio_list(), there are actually three cases (something
different is done for incompletely invalidated buffers), but
filemap_release_folio() elides two of them.
In shrink_active_list(), we don't have have the folio lock yet, so the
check allows us to avoid locking the page unnecessarily.
A wrapper function to check if a folio needs release is provided for those
places that still need to do it in the mm/ directory. This will acquire
additional parts to the condition in a future patch.
After this, the only remaining caller of folio_has_private() outside of
mm/ is a check in fuse.
Link: https://lkml.kernel.org/r/20230628104852.3391651-1-dhowells@redhat.com
Link: https://lkml.kernel.org/r/20230628104852.3391651-2-dhowells@redhat.com
Reported-by: Rohith Surabattula <rohiths.msft@gmail.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steve French <sfrench@samba.org>
Cc: Shyam Prasad N <nspmangalore@gmail.com>
Cc: Rohith Surabattula <rohiths.msft@gmail.com>
Cc: Dave Wysochanski <dwysocha@redhat.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Xiubo Li <xiubli@redhat.com>
Cc: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
ext4_double_up_write_data_sem(orig_inode, donor_inode);
goto data_copy;
}
- if ((folio_has_private(folio[0]) &&
- !filemap_release_folio(folio[0], 0)) ||
- (folio_has_private(folio[1]) &&
- !filemap_release_folio(folio[1], 0))) {
+ if (!filemap_release_folio(folio[0], 0) ||
+ !filemap_release_folio(folio[1], 0)) {
*err = -EBUSY;
goto drop_data_sem;
}
/* At this point all buffers in range are uptodate, old mapping layout
* is no longer required, try to drop it now. */
- if ((folio_has_private(folio[0]) &&
- !filemap_release_folio(folio[0], 0)) ||
- (folio_has_private(folio[1]) &&
- !filemap_release_folio(folio[1], 0))) {
+ if (!filemap_release_folio(folio[0], 0) ||
+ !filemap_release_folio(folio[1], 0)) {
*err = -EBUSY;
goto unlock_folios;
}
*/
folio_wait_writeback(folio);
- if (folio_has_private(folio) &&
- !filemap_release_folio(folio, GFP_KERNEL))
+ if (!filemap_release_folio(folio, GFP_KERNEL))
goto out_unlock;
/*
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;
gfp = current_gfp_context(mapping_gfp_mask(mapping) &
GFP_RECLAIM_MASK);
- if (folio_test_private(folio) &&
- !filemap_release_folio(folio, gfp)) {
+ if (!filemap_release_folio(folio, gfp)) {
ret = -EBUSY;
goto out;
}
set_page_count(page, 1);
}
+/*
+ * Return true if a folio needs ->release_folio() calling upon it.
+ */
+static inline bool folio_needs_release(struct folio *folio)
+{
+ return folio_has_private(folio);
+}
+
extern unsigned long highest_memmap_pfn;
/*
goto out_unlock;
}
- if (folio_has_private(folio) &&
- !filemap_release_folio(folio, GFP_KERNEL)) {
+ if (!filemap_release_folio(folio, GFP_KERNEL)) {
result = SCAN_PAGE_HAS_PRIVATE;
folio_putback_lru(folio);
goto out_unlock;
struct folio *folio = page_folio(p);
int err = mapping->a_ops->error_remove_page(mapping, p);
- if (err != 0) {
+ if (err != 0)
pr_info("%#lx: Failed to punch page: %d\n", pfn, err);
- } else if (folio_has_private(folio) &&
- !filemap_release_folio(folio, GFP_NOIO)) {
+ else if (!filemap_release_folio(folio, GFP_NOIO))
pr_info("%#lx: failed to release buffers\n", pfn);
- } else {
+ else
ret = MF_RECOVERED;
- }
} else {
/*
* If the file system doesn't support it just invalidate
* Buffers may be managed in a filesystem specific way.
* We must have no buffers or drop them.
*/
- if (folio_test_private(src) &&
- !filemap_release_folio(src, GFP_KERNEL))
+ if (!filemap_release_folio(src, GFP_KERNEL))
return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
return migrate_folio(mapping, dst, src, mode);
#include <linux/highmem.h>
#include <linux/pagevec.h>
#include <linux/task_io_accounting_ops.h>
-#include <linux/buffer_head.h> /* grr. try_to_release_page */
#include <linux/shmem_fs.h>
#include <linux/rmap.h>
#include "internal.h"
if (folio_ref_count(folio) >
folio_nr_pages(folio) + folio_has_private(folio) + 1)
return 0;
- if (folio_has_private(folio) && !filemap_release_folio(folio, 0))
+ if (!filemap_release_folio(folio, 0))
return 0;
return remove_mapping(mapping, folio);
if (folio->mapping != mapping)
return 0;
- if (folio_has_private(folio) &&
- !filemap_release_folio(folio, GFP_KERNEL))
+ if (!filemap_release_folio(folio, GFP_KERNEL))
return 0;
spin_lock(&mapping->host->i_lock);
* (refcount == 1) it can be freed. Otherwise, leave
* the folio on the LRU so it is swappable.
*/
- if (folio_has_private(folio)) {
+ if (folio_needs_release(folio)) {
if (!filemap_release_folio(folio, sc->gfp_mask))
goto activate_locked;
if (!mapping && folio_ref_count(folio) == 1) {
}
if (unlikely(buffer_heads_over_limit)) {
- if (folio_test_private(folio) && folio_trylock(folio)) {
- if (folio_test_private(folio))
- filemap_release_folio(folio, 0);
+ if (folio_needs_release(folio) &&
+ folio_trylock(folio)) {
+ filemap_release_folio(folio, 0);
folio_unlock(folio);
}
}