linux-kernel - [PATCH 5.14 153/169] mm/thp: decrease nr

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Message-Id: <20211025191036.865976319@linuxfoundation.org>
Date:   Mon, 25 Oct 2021 21:15:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>, sfoon.kim@...sung.com,
        Song Liu <songliubraving@...com>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hillf Danton <hdanton@...a.com>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.14 153/169] mm/thp: decrease nr_thps in files mapping on THP split

From: Marek Szyprowski <m.szyprowski@...sung.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@...sung.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@...radead.org>
Reviewed-by: Yang Shi <shy828301@...il.com>
Cc: <sfoon.kim@...sung.com>
Cc: Song Liu <songliubraving@...com>
Cc: Rik van Riel <riel@...riel.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Hillf Danton <hdanton@...a.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: William Kucharski <william.kucharski@...cle.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.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