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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Meta kernel team , 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() Message-Id: <20260129105015.0ed043764a4ad220334b7ae1@linux-foundation.org> In-Reply-To: <20260129184054.910897-1-shakeel.butt@linux.dev> References: <20260129184054.910897-1-shakeel.butt@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Stat-Signature: ac6j8r8akgezwguq41x6ds8tkcgeu1uq X-Rspam-User: X-Rspamd-Queue-Id: CD8C01C000D X-HE-Tag: 1769712617-157143 X-HE-Meta: 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 GQVt8SRV hVMuthMZ72pXoNpjRbnzaTqdrSQbtJXJHgUSquAx0Z7y74FX0xwBJ+sbaMUN5noVzzMrsYTQVlm6ZtlOO2W5xGBnf+sXOXXJ4NTAfv6hOf+q1SZDnbUXd7X3sBTtYypT/JLax3NiaeN6vY3HXFwh7wTWteLWYWqeuql4O0Wyol4ffWnmxtjOhpwOCyume7q74EtLiBGxtqSw1m2GYiBF8+qdTS4utQas/h0FD7rYLZqKUBbnIM4kLaoRW0Mgirsy/pHYJ4WfL2xm7vg3Mj+balPF8Zvk0vaLJmrZaGczMP5Ppyu8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 29 Jan 2026 10:40:54 -0800 Shakeel Butt 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? > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Should we cc:stable?