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Wed, 26 Aug 2026 21:45:56 +0000 X-Mizu-Trace-ID: f36f976b6e63a41b X-Migadu-Flow: FLOW_OUT Date: Wed, 26 Aug 2026 14:45:54 -0700 From: Shakeel Butt To: Tao Cui Cc: tj@kernel.org, akpm@linux-foundation.org, mhocko@suse.com, mhocko@kernel.org, mkoutny@suse.com, hannes@cmpxchg.org, roman.gushchin@linux.dev, muchun.song@linux.dev, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Tao Cui Subject: Re: [PATCH v2] docs: cgroup: document empty-write behavior of memory limit knobs Message-ID: References: <20260826021753.197871-1-cui.tao@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260826021753.197871-1-cui.tao@linux.dev> X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C0ED440003 X-Stat-Signature: x7ecuy9fr9ckjym9rpz3zaanh3sp565t X-HE-Tag: 1787780757-733529 X-HE-Meta: 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 G/Drrpvd drfzuNkkP392vPmtFfuF/YXfNO1HwIAKxGn2R7gZsl7j0PgH2OhhGUPquQ5RO3W1qCNMncyMEkU3uUAe2f5Yr7v590w20lgEeoI0OjTMpy9ch2VmIumazga1dMjBhyFIdWYbWH+09qMfAB95Yvmqk0ZIHo4bWr9ov/MhSTbdZ9InDavvOg1qpN7on0kWmDqWnaKMTuVMY3oNkuQw+4dFUGN03mFhn5vWbMx4M1SPvxleV1MPJG0Kbglnh+/f3qBpoV6sJQmalMYSU8XS7IP5e3k0lHYcT0O2O4FQluEyh8D4jG4gh6V/a7LqKzCQ3L4f4k1g/2zKAYXJNUQIbJRrpXpL8Jg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 26, 2026 at 10:17:53AM +0800, Tao Cui wrote: > From: Tao Cui > > A maintenance script on a cluster wrote an unset variable into > memory.max of a workload cgroup; the variable expanded to an empty > string, the write succeeded, and the workload in the cgroup was > OOM-killed. Nothing pointed back at the write, so it took quite > some time to trace the OOM kills to that script. > > The memory controller documentation does not say what an empty > write does; the cpuset controller documents its empty-value > semantics. The actual behavior is that the empty string is > accepted as 0. Reproduced on a k8s cluster (v1.29, cgroup v2, > two-container pod, 384M limit): > > # LIMIT= > # echo "$LIMIT" > $CG/memory.max > # echo $? > 0 > > m6demo 0/2 OOMKilled 0 > > Memory cgroup out of memory: Killed process 339529 (sleep) ... anon-rss:32kB > > State it where the interface files are introduced, alongside the > existing notes on units and page rounding. > > Link: https://lore.kernel.org/all/aoVUlFdZYLFn_gvJ@tiehlicka/ > Signed-off-by: Tao Cui Acked-by: Shakeel Butt