From: Shakeel Butt <shakeel.butt@linux.dev>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@surriel.com>,
Song Liu <songliubraving@fb.com>,
Kiryl Shutsemau <kas@kernel.org>,
Usama Arif <usamaarif642@gmail.com>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
Nico Pache <npache@redhat.com>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>,
Lance Yang <lance.yang@linux.dev>,
Meta kernel team <kernel-team@meta.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: khugepaged: fix NR_FILE_PAGES accounting in collapse_file()
Date: Thu, 29 Jan 2026 10:55:14 -0800 [thread overview]
Message-ID: <aXusxKTW5Y6-0qKO@linux.dev> (raw)
In-Reply-To: <20260129105015.0ed043764a4ad220334b7ae1@linux-foundation.org>
On Thu, Jan 29, 2026 at 10:50:15AM -0800, Andrew Morton wrote:
> On Thu, 29 Jan 2026 10:40:54 -0800 Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> > In META's fleet, we are seeing high level cgroups with zero file memcg
> > stat but their descendants have non-zero file stat. This should not be
> > possible. On further inspection by looking at kernel data structures
> > though drgn, it was revealed that the high level cgroups have negative
> > file stat which was aggregated from their children.
> >
> > Another interesting point was that this specific issue start happening
> > more often as we started deploying thp-always more widely which
> > indicates some correlation between file memory and THPs and indeed it
> > was found that file memcg stat accounting is buggy in the collapse code
> > path from the start.
>
> So this has no known runtime effect apart from incorrect accounting?
Yes just an accounting bug.
>
> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
>
> Should we cc:stable?
I think so.
next prev parent reply other threads:[~2026-01-29 18:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-29 18:40 [PATCH] mm: khugepaged: fix NR_FILE_PAGES accounting in collapse_file() Shakeel Butt
2026-01-29 18:50 ` Andrew Morton
2026-01-29 18:55 ` Shakeel Butt [this message]
2026-01-29 22:47 ` Matthew Wilcox
2026-01-30 0:47 ` Shakeel Butt
2026-01-29 22:49 ` Usama Arif
2026-01-30 0:32 ` Johannes Weiner
2026-01-30 0:50 ` Shakeel Butt
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