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From: Shakeel Butt To: Tejun Heo Cc: Roman Gushchin , Andrew Morton , Johannes Weiner , Michal Hocko , Muchun Song , Alexei Starovoitov , Peilin Ye , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH] memcg: skip cgroup_file_notify if spinning is not allowed Message-ID: References: <20250905201606.66198-1-shakeel.butt@linux.dev> <87y0qsa95d.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 1edrznbcrib4dw3tkabswcfrufrsmo6e X-Rspam-User: X-Rspamd-Queue-Id: 1F60340006 X-Rspamd-Server: rspam05 X-HE-Tag: 1757108108-748670 X-HE-Meta: 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 Qn9NcC1d hiF6EtXBlOXb4I0N7Tx7+AYXO3G9oi/zwNOM6wH1X1Xv8+Tl+YQZxaPDVYCMpnwzMZ+8YaRNx1TLxjauSgOTD0mzmzyfRn0/QcIn5TX3Em+bOTwyFKLsjYj1bIHyr8htIhN1PLlSA6Vo127I8qnn1J/B8RkXb5LQFKnCwFlOpRuHWbYDzKSVftf/s/YtzzGnNKWVI3Lf8Hws0GIJVEYxBKVCXQqsOf1UYw3KvoWgJypOC7SPTXBT8MkGXEunt8czI2ou8 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 Fri, Sep 05, 2025 at 11:25:34AM -1000, Tejun Heo wrote: > On Fri, Sep 05, 2025 at 02:20:46PM -0700, Roman Gushchin wrote: > > Shakeel Butt writes: > > > > > Generally memcg charging is allowed from all the contexts including NMI > > > where even spinning on spinlock can cause locking issues. However one > > > call chain was missed during the addition of memcg charging from any > > > context support. That is try_charge_memcg() -> memcg_memory_event() -> > > > cgroup_file_notify(). > > > > > > The possible function call tree under cgroup_file_notify() can acquire > > > many different spin locks in spinning mode. Some of them are > > > cgroup_file_kn_lock, kernfs_notify_lock, pool_workqeue's lock. So, let's > > > just skip cgroup_file_notify() from memcg charging if the context does > > > not allow spinning. > > > > Hmm, what about OOM events? Losing something like MEMCG_LOW doesn't look > > like a bit deal, but OOM events can be way more important. > > > > Should we instead preserve the event (e.g. as a pending_event_mask) and > > raise it on the next occasion / from a different context? > > Maybe punt with an irq_work? Oh good suggestion, I will check irq_work as well. Though I think that can be a followup work.