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Thu, 12 Nov 2026 02:27:11 +0000 X-Mizu-Trace-ID: 6e62475f303e8754 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii X-Archived-By: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.200.71.1.16\)) Subject: Re: [PATCH] memcg: flush nr_charged_bytes when the obj stock trylock fails From: Muchun Song In-Reply-To: <20261112013220.4064478-1-shakeel.butt@linux.dev> Date: Thu, 12 Nov 2026 10:26:56 +0800 Cc: Andrew Morton , Johannes Weiner , David Hildenbrand , Michal Hocko , Roman Gushchin , Vlastimil Babka , Meta kernel team , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org Content-Transfer-Encoding: 7bit Message-Id: <16F05AF0-BF45-4206-8B42-0D2AD6CA2B20@linux.dev> References: <20261112013220.4064478-1-shakeel.butt@linux.dev> To: Shakeel Butt X-Mailer: Apple Mail (2.3901.200.71.1.16) X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EC9A8C0004 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: g1ns53q4qz1c8yq8ffpqu73x8aof4g8p X-HE-Tag: 1794450433-353579 X-HE-Meta: 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 D1sVLOOC GUF+WqBoNt3HewDgDtMNiQRUpxL1RjrOpMeMIrRT35aPLtUESjYJTDldBjKaG88lhKcLZX6uovWLqHXeCc4wT+dpCuQLJO2ZoWMiUMoMFRqppvQ9I4Ye2J7KvSjiM7F9HCWoFn2WROrVKmp+RaCyAdpqZs71fHF17JRmZjB7cQn6v7Gopkoc5IQGogZanFfi/4AWwx/+XiTvMYkNP8URTQdg82NwYJNUVp5pXVmB+ogr/yp+4HzL+59xODGsS6KLWFFOirhjsP3mBNMnM3kzF/35yGO6S00TUPrbwLYoYc5IoIIW9/C6wUIiDUM69zCsIPc4vdiE9AUlnwX8NLH3M3U+XmxoewkH/YsyEYAqlNFc03+VuJCKriJ64Cg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 > On Nov 12, 2026, at 09:32, Shakeel Butt wrote: > > When interrupt code, such as an RCU callback in softirq, runs on top of > a task that holds the obj stock lock, its trylock fails and the bytes go > to objcg->nr_charged_bytes. Nothing empties that counter while every CPU > using the objcg keeps it in its stock, so it can grow without limit. > > Users see memory.current and the "kernel" field of memory.stat keep > growing while the cgroup's real usage does not. With memory.high or > memory.max set, the cgroup is reclaimed, throttled or even OOM-killed > for memory it does not use. The counter is 32-bit, so after 4 GiB it > wraps, and those 4 GiB stay charged to the cgroup and its ancestors > until reboot, even after the cgroup is removed. > > Fix it by uncharging the whole pages in nr_charged_bytes whenever the > trylock fails. > > Fixes: 200577f69f29 ("memcg: objcg stock trylock without irq disabling") > Reported-by: Chris Mason > Signed-off-by: Shakeel Butt > Cc: stable@vger.kernel.org Acked-by: Muchun Song (ByteDance) Thanks.