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From: Shakeel Butt To: Alexei Starovoitov Cc: Andrew Morton , Tejun Heo , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Alexei Starovoitov , Peilin Ye , Kumar Kartikeya Dwivedi , bpf , linux-mm , "open list:CONTROL GROUP (CGROUP)" , LKML , 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> <5qi2llyzf7gklncflo6gxoozljbm4h3tpnuv4u4ej4ztysvi6f@x44v7nz2wdzd> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: B07C340006 X-Stat-Signature: n6o1mjge3ep6rq686j4wodxotn95y71e X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1758342708-932470 X-HE-Meta: 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 j0adNY4o sS1ZEfxNL8bVbACNfW6cjsAwPa1dpTbl72IcG5UVNfCi7TfAUgB68y0XSWSSAPlXiT+nWENmM8ZPZzktFH5YqVHDcVkVeSnHPdcI5bRQFiEF/2QS2JMD9rreWBrRJ5pQ/kPQkezX9XciPMhUh7mcUDBi6G9yz3JMApZ729yiywtLrKalhOqSXuEbRRuMHHpGlHlqo1Fm88pFn5Dpo4GrfAqXichdKeul5SWeU+51PhX6o0Ttz6V7hIrF5XxAxqhLTCNX3z3oSOorN+L6DzZB6xXwncXpWht7NebUJP6RlhvU5gEixaue/X7LobQ== 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 19, 2025 at 07:47:57PM -0700, Alexei Starovoitov wrote: > On Thu, Sep 18, 2025 at 7:49 PM Shakeel Butt wrote: > > [...] > > + > > +static DEFINE_PER_CPU(struct defer_memcg_events, postpone_events) = { > > + .memcg_llist = LLIST_HEAD_INIT(memcg_llist), > > + .work = IRQ_WORK_INIT(process_deferred_events), > > +}; > > Why all these per cpu stuff ? I don't understand what it helps with. > To have max_events per-cpu? > Just one global llist and irq_work will do just fine. > and global max_events too. Right, global llist and irq_work will work but max_events has to be per-memcg. In addition we will need llist_node per-memcg and I think we will need to do a similar cmpxchg trick I did in css_rstat_updated() to eliminate the potential race of llist_node of a given memcg i.e. multiple CPUs trying to add llist_node of a memcg to the global llist. This can work but I am still debating if this additional complexity is worth it as compared to the original patch where we skip cgroup_file_notify() for !allow_spinning condition.