mm: merge folio_has_private()/filemap_release_folio() call pairs

[ Upstream commit 0201ebf274a306a6ebb95e5dc2d6a0a27c737cac ]

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>
Stable-dep-of: 1898efcdbed3 ("block: update the stable_writes flag in bdev_add")
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 8dbb87edf24c49b9a31c53b5c44fce301fb9eb1b..dedc9d445f24337476b5a47cb67addec0d44851d 100644 (file)
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -339,10 +339,8 @@ 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;
                }
@@ -361,10 +359,8 @@ 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;
        }

diff --git a/fs/splice.c b/fs/splice.c
index c4ae54deac42c000691816c2880597837cb48c42..d0230cf8ec5711eb21b55f63151e5485f34904de 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -65,8 +65,7 @@ static bool page_cache_pipe_buf_try_steal(struct pipe_inode_info *pipe,
                 */
                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;
 
                /*

diff --git a/mm/filemap.c b/mm/filemap.c
index 10fe6430693bdb05a644be3d8e1f397d4e38a7eb..2809b1174f04e82b55045a5ab5aa0593ca4219ee 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4005,6 +4005,8 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
        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;
 

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2753fb54cdf380e0984d4558e353ac3f32137925..59577946735b1f906e90106174e6a5fb7e853713 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2694,8 +2694,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
                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;
                }

diff --git a/mm/internal.h b/mm/internal.h
index 6b7ef495b56d3d9ef383f5b63db2c1a28ed44c20..1fefb5181ab783175344aed7740a56aa7af1e342 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -163,6 +163,14 @@ static inline void set_page_refcounted(struct page *page)
        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;
 
 /*

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6fc7db587c4538aa4a24a508ec349ca90950ec7b..65bd0b105266a8de7705605a262919059ca3de05 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1955,8 +1955,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
                        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;

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 6355166a6bb2807a760e4971a91be85556c349e9..5b846ed5dcbe91aff726b461971fe7741a998aca 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -830,14 +830,12 @@ static int truncate_error_page(struct page *p, unsigned long pfn,
                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

diff --git a/mm/migrate.c b/mm/migrate.c
index 91bd69c61148e01e1f67b921080f1d7e365515b4..c93dd6a31c31a4f21cee7751f5d1bea53d396feb 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -914,8 +914,7 @@ static int fallback_migrate_folio(struct address_space *mapping,
         * 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);

diff --git a/mm/truncate.c b/mm/truncate.c
index c0be77e5c0083c6b993dd39247dd203e0ff627da..0d4dd233f518721a8a5b6514c93025313c8f7a66 100644 (file)
--- a/mm/truncate.c
+++ b/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 address_space *mapping,
        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);
@@ -581,8 +580,7 @@ static int invalidate_complete_folio2(struct address_space *mapping,
        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);

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3f090faa6377ff4390fd501d11348d8e528c1839..9f3cfb7caa48d0cb4e704394a008e2b91c1e2b78 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1992,7 +1992,7 @@ 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) {
@@ -2618,9 +2618,9 @@ static void shrink_active_list(unsigned long nr_to_scan,
                }
 
                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);
                        }
                }