Re: [PATCH v3] mm: Fix for negative counter: nr_file_hugepages

[Matthew Wilcox]

On Wed, Nov 08, 2023 at 09:15:17AM -0800, Stefan Roesch wrote:
> 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.
> 
> Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
> Co-debugged-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>