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b=OrbE4PEdyLw5DXjC4jcVD/Tri+x0F2xafcSrTG6gZSBwEEnwX7hQq0Nbs26c3junY EWq9jV80bGcJyrkrcmdCQ9jtbwZ/alCT7O1sUn57Va/TUcca+V6cydKzNTblpHA0C2 zycxKNEimZNI9MGugDKAfwwQT4qxQrJdwDFprQdE= Date: Sun, 4 Oct 2026 23:36:15 -0700 From: Andrew Morton To: Vernon Yang Cc: david@kernel.org, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, hannes@cmpxchg.org, mhocko@kernel.org, ljs@kernel.org, roman.gushchin@linux.dev, dave@stgolabs.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang , stable@vger.kernel.org Subject: Re: [PATCH] mm: vmscan: don't count per-node proactive reclaim as memory pressure Message-Id: <20261004233615.df26e580c1bc916c7f3a23b2@linux-foundation.org> In-Reply-To: <20261005062236.564210-1-vernon2gm@gmail.com> References: <20261005062236.564210-1-vernon2gm@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (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: rspam05 X-Rspamd-Queue-Id: 34450A0006 X-Stat-Signature: u3uh9tp8rexii9n6wyit4c4xt4pbzuf9 X-Rspam-User: X-HE-Tag: 1791182177-202766 X-HE-Meta: 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 ciaoCH/R yHUkfQHN7E7Vmt8EmXXFrYap7H4YW/lW5SsuVzGjG6aFyla1HHtWpat6C4ekjeU/9amaNhAXEcGZIWFCHQhTvsmK8H1vUszEaLyoaiSKH83p6eYlefNwFVQs9/AIPZRRK1hIBbHZqwXT1CBTytBXFFouBYtvNoEFZMM7ALStl0SxjlRzELW872TT0YkcYl65sZjEGEvNf12nCoalF7rmG4nRfp3WyOIZSQgG1HzZwp+0sTJNVm7a674px9Skz8Ad3g+q1ts2sqMle2D+/w1YDB4oDJQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 5 Oct 2026 14:22:36 +0800 Vernon Yang wrote: > When the cgroup has no memory pressure at all, writing to > /sys/devices/system/nodeX/reclaim triggers proactive reclaim on > NUMA node, causing increase in the writer cgroup's memory PSI. > > Due to this reclaim is performed in the context of the write(), > accounted as memory pressure on the writer, like > commit e22c6ed90aa9 ("mm: memcontrol: don't count limit-setting reclaim > as memory pressure"). This is unexpected, the phenomenon resembling > senpai will appear again. What is this? > The Documentation/ABI/stable/sysfs-devices-node documentation also > notes that "This interface is equivalent to the memcg variant." > > This patch unifies the semantics of the memcg and node interfaces: > per-node proactive reclaim is no longer counted as memory pressure, > and the per-node proactive reclaim interface no longer produces > phantom pressure. > > I ran demo[1] that performs per-node proactive reclaim 10000 times > in qemu, writer cgroup memory.pressure as follows: > > without patch: > > some avg10=31.53 avg60=13.42 avg300=3.31 total=10602985 > full avg10=31.53 avg60=13.42 avg300=3.31 total=10602985 > > with patch: > > some avg10=9.59 avg60=3.41 avg300=0.81 total=2686221 > full avg10=9.59 avg60=3.41 avg300=0.81 total=2686221