[18/19] mm/thp: decrease nr_thps in file's mapping on THP split

Commit Message

Andrew Morton Oct. 18, 2021, 10:16 p.m. UTC

From: Marek Szyprowski <[e-mail]>
Subject: mm/thp: decrease nr_thps in file's mapping on THP split

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, where one runs a big binary, kernel remaps it
with THPs, then one forces 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/[e-mail]
Signed-off-by: Marek Szyprowski <[e-mail]>
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) <[e-mail]>
Reviewed-by: Yang Shi <[e-mail]>
Cc: <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Hillf Danton <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: William Kucharski <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/huge_memory.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patch

--- a/mm/huge_memory.c~mm-thp-decrease-nr_thps-in-files-mapping-on-thp-split
+++ a/mm/huge_memory.c
@@ -2700,12 +2700,14 @@  int split_huge_page_to_list(struct page
 		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);