The patch titled Subject: mm: fix for negative counter: nr_file_hugepages has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-fix-for-negative-counter-nr_file_hugepages.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Stefan Roesch shr@devkernel.io Subject: mm: fix for negative counter: nr_file_hugepages Date: Mon, 6 Nov 2023 10:19:18 -0800

While qualifiying the 6.4 release, the following warning was detected in messages:

vmstat_refresh: nr_file_hugepages -15664

The warning is caused by the incorrect updating of the NR_FILE_THPS counter in the function split_huge_page_to_list. The if case is checking for folio_test_swapbacked, but the else case is missing the check for folio_test_pmd_mappable. The other functions that manipulate the counter like __filemap_add_folio and filemap_unaccount_folio have the corresponding check.

I have a test case, which reproduces the problem. It can be found here: https://github.com/sroeschus/testcase/blob/main/vmstat_refresh/madv.c

The test case reproduces on an XFS filesystem. Running the same test case on a BTRFS filesystem does not reproduce the problem.

AFAIK version 6.1 until 6.6 are affected by this problem.

Link: https://lkml.kernel.org/r/20231106181918.1091043-1-shr@devkernel.io Signed-off-by: Stefan Roesch shr@devkernel.io Co-debugged-by: Johannes Weiner hannes@cmpxchg.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Rik van Riel riel@surriel.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/huge_memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/huge_memory.c~mm-fix-for-negative-counter-nr_file_hugepages +++ a/mm/huge_memory.c @@ -2772,7 +2772,8 @@ int split_huge_page_to_list(struct page if (folio_test_swapbacked(folio)) { __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr); - } else { + } else if (folio_test_pmd_mappable(folio)) { + __lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr); filemap_nr_thps_dec(mapping); _

Patches currently in -mm which might be from shr@devkernel.io are

mm-fix-for-negative-counter-nr_file_hugepages.patch