linux-kernel - Re: [PATCH v3] mm: Fix for negative counter: nr_file

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Message-ID: <ZUvFjzqTXg3WU2Q6@casper.infradead.org>
Date:   Wed, 8 Nov 2023 17:29:51 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Stefan Roesch <shr@...kernel.io>
Cc:     kernel-team@...com, akpm@...ux-foundation.org, hannes@...xchg.org,
        riel@...riel.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] mm: Fix for negative counter: nr_file_hugepages

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@...kernel.io>
> Co-debugged-by: Johannes Weiner <hannes@...xchg.org>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Cc: stable@...r.kernel.org

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>