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b=pTMVo+nj7csww0q3/7UDygDGBnLo3Te9cgJKYwUtiPgeHpi4Cwdke/MPEfT9PnXLX DXeGEdvIfwsnOf+3RoWJNjmYPfdUYmGAVQd6LMP8N0/qkM1IOGHaiWl/Sl0aHaTn82 E4k7BPsCffyuL2niZV8EMfcE27uUOPkaH9zmFSAw= Date: Mon, 22 Sep 2025 16:03:08 -0700 From: Andrew Morton To: Shakeel Butt Cc: Tejun Heo , Johannes Weiner , Michal Hocko , Roman Gushchin , 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 , Michal Hocko Subject: Re: [PATCH v2] memcg: skip cgroup_file_notify if spinning is not allowed Message-Id: <20250922160308.524be6ba4d418886095ab223@linux-foundation.org> In-Reply-To: <20250922220203.261714-1-shakeel.butt@linux.dev> References: <20250922220203.261714-1-shakeel.butt@linux.dev> X-Mailer: Sylpheed 3.7.0 (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: rspam12 X-Rspamd-Queue-Id: E7BE11C0014 X-Stat-Signature: ydnpf36xizxze91iwkoicjxdct64j8hg X-Rspam-User: X-HE-Tag: 1758582190-575248 X-HE-Meta: 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 YbxgoYn3 l8zUX15lTr33RcImQXXYCbot0df12wP+uY3iQZ/qIoHLc7Lehq/XhtjePhHQ9DAGSJyUP0R9VQwsSREpLWtZr2rJ2eVlF0ufSt8xGEmKPGEusHG4RuglygIruPWaK+Jo2g1q/yyHMsO33I6tKXaSzShMDzMycWyd1OVRb9GIlfjPBSWorgRWrcDfnqn+DVFrILVBApnb3jEIdHjss/7eyoSGwQ9INfDFTLbBqQFoc8Z++rOb/IwbBSRyOqZiwgk8DBbq2KYrPDI2QA5hnp8+hv6WSz2m2j1UTf6btj8BbXPtZZJc= 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 Mon, 22 Sep 2025 15:02:03 -0700 Shakeel Butt wrote: > 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. > > Alternative approach was also explored where instead of skipping > cgroup_file_notify(), we defer the memcg event processing to irq_work > [1]. However it adds complexity and it was decided to keep things simple > until we need more memcg events with !allow_spinning requirement. What are the downsides here? Inaccurate charging obviously, but how might this affect users? > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2307,12 +2307,13 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > bool drained = false; > bool raised_max_event = false; > unsigned long pflags; > + bool allow_spinning = gfpflags_allow_spinning(gfp_mask); > Does this affect only the problematic call chain which you have identified, or might other callers be undesirably affected?