mm/mincore, swap: consolidate swap cache checking for mincore

Patch series "mm/mincore: minor clean up for swap cache checking".

This series cleans up a swap cache helper only used by mincore, move it
back into mincore code.  Also separate the swap cache related logics out
of shmem / page cache logics in mincore.

With this series we have less lines of code and better performance.

Before this series:
mincore on a swaped out 16G anon mmap range:
Took 488220 us
mincore on 16G shmem mmap range:
Took 530272 us.

After this series:
mincore on a swaped out 16G anon mmap range:
Took 446763 us
mincore on 16G shmem mmap range:
Took 460496 us.

About ~10% faster.


This patch (of 2):

The filemap_get_incore_folio (previously find_get_incore_page) helper was
introduced by commit 61ef18655704 ("mm: factor find_get_incore_page out of
mincore_page") to be used by later commit f5df8635c5a3 ("mm: use
find_get_incore_page in memcontrol"), so memory cgroup charge move code
can be simplified.

But commit 6b611388b626 ("memcg-v1: remove charge move code") removed that
user completely, it's only used by mincore now.

So this commit basically reverts commit 61ef18655704 ("mm: factor
find_get_incore_page out of mincore_page").  Move it back to mincore side
to simplify the code.

Link: https://lkml.kernel.org/r/20250811172018.48901-1-ryncsn@gmail.com
Link: https://lkml.kernel.org/r/20250811172018.48901-2-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 27 insertions, 2 deletions

diff --git a/mm/mincore.c b/mm/mincore.c
index 10dabefc3acc..20fd0967d3cb 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -64,8 +64,33 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
 	 * any other file mapping (ie. marked !present and faulted in with
 	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
 	 */
-	folio = filemap_get_incore_folio(mapping, index);
-	if (!IS_ERR(folio)) {
+	if (IS_ENABLED(CONFIG_SWAP) && shmem_mapping(mapping)) {
+		folio = filemap_get_entry(mapping, index);
+		/*
+		 * shmem/tmpfs may return swap: account for swapcache
+		 * page too.
+		 */
+		if (xa_is_value(folio)) {
+			struct swap_info_struct *si;
+			swp_entry_t swp = radix_to_swp_entry(folio);
+			/* There might be swapin error entries in shmem mapping. */
+			if (non_swap_entry(swp))
+				return 0;
+			/* Prevent swap device to being swapoff under us */
+			si = get_swap_device(swp);
+			if (si) {
+				folio = filemap_get_folio(swap_address_space(swp),
+							  swap_cache_index(swp));
+				put_swap_device(si);
+			} else {
+				return 0;
+			}
+		}
+	} else {
+		folio = filemap_get_folio(mapping, index);
+	}
+
+	if (!IS_ERR_OR_NULL(folio)) {
 		present = folio_test_uptodate(folio);
 		folio_put(folio);
 	}