The patch titled
Subject: mm: merge folio_has_private()/filemap_release_folio() call pairs
has been added to the -mm mm-unstable branch. Its filename is
mm-merge-folio_has_private-filemap_release_folio-call-pairs.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-merge-folio_has_private-filemap_release_folio-call-pairs.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Howells <dhowells@xxxxxxxxxx>
Subject: mm: merge folio_has_private()/filemap_release_folio() call pairs
Date: Wed, 28 Jun 2023 11:48:51 +0100
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@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20230628104852.3391651-2-dhowells@xxxxxxxxxx
Reported-by: Rohith Surabattula <rohiths.msft@xxxxxxxxx>
Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Steve French <sfrench@xxxxxxxxx>
Cc: Shyam Prasad N <nspmangalore@xxxxxxxxx>
Cc: Rohith Surabattula <rohiths.msft@xxxxxxxxx>
Cc: Dave Wysochanski <dwysocha@xxxxxxxxxx>
Cc: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>
Cc: Ilya Dryomov <idryomov@xxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: Xiubo Li <xiubli@xxxxxxxxxx>
Cc: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ext4/move_extent.c | 12 ++++--------
fs/splice.c | 3 +--
mm/filemap.c | 2 ++
mm/huge_memory.c | 3 +--
mm/internal.h | 8 ++++++++
mm/khugepaged.c | 3 +--
mm/memory-failure.c | 8 +++-----
mm/migrate.c | 3 +--
mm/truncate.c | 6 ++----
mm/vmscan.c | 8 ++++----
10 files changed, 27 insertions(+), 29 deletions(-)
--- a/fs/ext4/move_extent.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/fs/ext4/move_extent.c
@@ -340,10 +340,8 @@ again:
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;
}
@@ -362,10 +360,8 @@ data_copy:
/* 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;
}
--- a/fs/splice.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/fs/splice.c
@@ -83,8 +83,7 @@ static bool page_cache_pipe_buf_try_stea
*/
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;
/*
--- a/mm/filemap.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/filemap.c
@@ -4074,6 +4074,8 @@ bool filemap_release_folio(struct folio
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;
--- a/mm/huge_memory.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/huge_memory.c
@@ -2697,8 +2697,7 @@ int split_huge_page_to_list(struct page
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;
}
--- a/mm/internal.h~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/internal.h
@@ -176,6 +176,14 @@ static inline void set_page_refcounted(s
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;
/*
--- a/mm/khugepaged.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/khugepaged.c
@@ -2078,8 +2078,7 @@ static int collapse_file(struct mm_struc
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;
--- a/mm/memory-failure.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/memory-failure.c
@@ -936,14 +936,12 @@ static int truncate_error_page(struct pa
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
--- a/mm/migrate.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/migrate.c
@@ -922,8 +922,7 @@ static int fallback_migrate_folio(struct
* 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);
--- a/mm/truncate.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/truncate.c
@@ -19,7 +19,6 @@
#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"
@@ -276,7 +275,7 @@ static long mapping_evict_folio(struct a
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);
@@ -573,8 +572,7 @@ static int invalidate_complete_folio2(st
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);
--- a/mm/vmscan.c~mm-merge-folio_has_private-filemap_release_folio-call-pairs
+++ a/mm/vmscan.c
@@ -2064,7 +2064,7 @@ retry:
* (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) {
@@ -2729,9 +2729,9 @@ static void shrink_active_list(unsigned
}
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);
}
}
_
Patches currently in -mm which might be from dhowells@xxxxxxxxxx are
mm-merge-folio_has_private-filemap_release_folio-call-pairs.patch
mm-netfs-fscache-stop-read-optimisation-when-folio-removed-from-pagecache.patch
