[PATCH 5.14 153/169] mm/thp: decrease nr_thps in files mapping on THP split

Greg Kroah-Hartman
2021-10-25T19:59:06Z

From: Marek Szyprowski <m.szyprowski@samsung.com>

[ Upstream commit 1ca7554d05ac038c98271f8968ed821266ecaa9c ]

Decrease nr_thps counter in file's mapping to ensure that the page cache
won't be dropped excessively on file write access if page has been
already split.

I've tried a test scenario running a big binary, kernel remaps it with
THPs, then force a THP split with /sys/kernel/debug/split_huge_pages.
During any further open of that binary with O_RDWR or O_WRITEONLY kernel
drops page cache for it, because of non-zero thps counter.

Link: https://lkml.kernel.org/r/20211012120237.2600-1-m.szyprowski@samsung.com
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: 09d91cda0e82 ("mm,thp: avoid writes to file with THP in pagecache")
Fixes: 06d3eff62d9d ("mm/thp: fix node page state in split_huge_page_to_list()")
Acked-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: <sfoon.kim@samsung.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/huge_memory.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index afff3ac87067..163c2da2a654 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2724,12 +2724,14 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
if (mapping) {
int nr = thp_nr_pages(head);

- if (PageSwapBacked(head))
+ if (PageSwapBacked(head)) {
__mod_lruvec_page_state(head, NR_SHMEM_THPS,
-nr);
- else
+ } else {
__mod_lruvec_page_state(head, NR_FILE_THPS,
-nr);
+ filemap_nr_thps_dec(mapping);
+ }
}

__split_huge_page(page, list, end);
--
2.33.0