linux-kernel - [PATCH] mm/thp: decrease nr_thps in file's mapping on THP split

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Date:   Tue, 12 Oct 2021 14:02:37 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        김성훈 <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>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: [PATCH] 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 splitted.

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()")
---
I've analyzed the code a few times but either I missed something or the
nr_thps counter is not decremented during the THP split on non-shmem file
pages.
---
 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 ec2bb93f7431..a6c2ba59abcd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2709,10 +2709,12 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		}
 		spin_unlock(&ds_queue->split_queue_lock);
 		if (mapping) {
-			if (PageSwapBacked(head))
+			if (PageSwapBacked(head)) {
 				__dec_node_page_state(head, NR_SHMEM_THPS);
-			else
+			} else {
 				__dec_node_page_state(head, NR_FILE_THPS);
+				filemap_nr_thps_dec(mapping);
+			}
 		}
 
 		__split_huge_page(page, list, end, flags);
-- 
2.17.1