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From: Shakeel Butt To: Usama Arif Cc: Andrew Morton , david@kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org, tj@kernel.org, mkoutny@suse.com, roman.gushchin@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, kernel-team@meta.com Subject: Re: [PATCH 1/2] mm/vmpressure: skip tree=true accounting on cgroup v2 Message-ID: References: <20260606114158.3126210-1-usama.arif@linux.dev> <20260606114158.3126210-2-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260606114158.3126210-2-usama.arif@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: 8fbr3bye6wm8cic6moxu1rq4pxbq378i X-Rspamd-Queue-Id: 5A5B81C0003 X-HE-Tag: 1780938410-554606 X-HE-Meta: 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 E7RtuaXv 0BORlVI8aYuhV+yU4u7mQk7jQgz5/5yfk8yT8Q9bUtRa7iE+0ao7P7efmGxU+SyDHRMtqO30pranXf3P0jYnr2Ui1G2/nogrDOhcW1E5xQWpeE2dgFxHc4QipjQf959KZrMOEXTdJxMqOclqsgjG4QTKovTmH7EYJWPphI5RF1YcmT1ODHEV1gdxol+iTF5UrXaFcIWceKhflXZbuIgc6UpBxuw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jun 06, 2026 at 04:41:33AM -0700, Usama Arif wrote: > vmpressure() has two outputs gated by the @tree argument: > > @tree=false drives in-kernel socket pressure (mem_cgroup_set_ > socket_pressure), consumed by TCP/SCTP. This only > applies on cgroup v2; on v1 socket memory is charged > separately via tcpmem and the consumer reads > memcg->tcpmem_pressure instead. > > @tree=true drives userspace eventfd notifications via the v1 > memory.pressure_level / cgroup.event_control interface. > v2 has no equivalent: userspace gets reclaim signals > through memory.pressure (PSI), which does not touch > vmpressure. > > The existing early return covered v1 + @tree=false. The symmetric > v2 + @tree=true case was falling through and doing the full lock / > accumulate / schedule_work / parent-walk dance for an events list > that can never be populated. bpftrace on a 176-core production host > (cgroup v2, CONFIG_MEMCG_V1=n, 285 memcgs, sustained reclaim) showed > ~16,200 @tree=true vmpressure() calls per minute. Add an early return > that skips cgroup v2 + tree = true which avoids us doing all this work. > On a v2-only host this also eliminates a lock contention path that can > serialise reclaimers on a single global sr_lock. > > Signed-off-by: Usama Arif Acked-by: Shakeel Butt