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From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Joonsoo Kim <js1304@gmail.com>,
        Alex Shi <alex.shi@linux.alibaba.com>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Hugh Dickins <hughd@google.com>,
        Michal Hocko <mhocko@suse.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Roman Gushchin <guro@fb.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
Subject: [PATCH 01/18] mm: fix NUMA node file count error in replace_page_cache()
Date:   Mon, 20 Apr 2020 18:11:09 -0400
Message-Id: <20200420221126.341272-2-hannes@cmpxchg.org>
In-Reply-To: <20200420221126.341272-1-hannes@cmpxchg.org>
References: <20200420221126.341272-1-hannes@cmpxchg.org>
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When replacing one page with another one in the cache, we have to
decrease the file count of the old page's NUMA node and increase the
one of the new NUMA node, otherwise the old node leaks the count and
the new node eventually underflows its counter.

Fixes: 74d609585d8b ("page cache: Add and replace pages using the XArray")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/filemap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 23a051a7ef0f..49e3b5da0216 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -808,11 +808,11 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
 	old->mapping = NULL;
 	/* hugetlb pages do not participate in page cache accounting. */
 	if (!PageHuge(old))
-		__dec_node_page_state(new, NR_FILE_PAGES);
+		__dec_node_page_state(old, NR_FILE_PAGES);
 	if (!PageHuge(new))
 		__inc_node_page_state(new, NR_FILE_PAGES);
 	if (PageSwapBacked(old))
-		__dec_node_page_state(new, NR_SHMEM);
+		__dec_node_page_state(old, NR_SHMEM);
 	if (PageSwapBacked(new))
 		__inc_node_page_state(new, NR_SHMEM);
 	xas_unlock_irqrestore(&xas, flags);
-- 
2.26.0