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>

8 files changed, 22 insertions, 19 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 10fe6430693b..2809b1174f04 100644
--- 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 2753fb54cdf3..59577946735b 100644
--- 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 6b7ef495b56d..1fefb5181ab7 100644
--- 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 6fc7db587c45..65bd0b105266 100644
--- 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 6355166a6bb2..5b846ed5dcbe 100644
--- 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 91bd69c61148..c93dd6a31c31 100644
--- 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 c0be77e5c008..0d4dd233f518 100644
--- 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 3f090faa6377..9f3cfb7caa48 100644
--- 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);
 			}
 		}