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Sat, 31 Oct 2026 16:53:43 +0000 X-Mizu-Trace-ID: a73ddf1f7291a74a X-Migadu-Flow: FLOW_OUT Date: Sat, 31 Oct 2026 09:53:38 -0700 From: Shakeel Butt To: Vernon Yang Cc: akpm@linux-foundation.org, david@kernel.org, kasong@tencent.com, qi.zheng@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 v2] mm: vmscan: don't count per-node proactive reclaim as memory pressure Message-ID: References: <20261012022917.1102467-1-vernon2gm@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261012022917.1102467-1-vernon2gm@gmail.com> X-Rspamd-Queue-Id: DB11240006 X-Stat-Signature: mshhhbaxqwyurg76osrs51gmaoz6y1m9 X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793465625-947584 X-HE-Meta: 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 CiIwHNou b/jUeitRPsnQAkJ7fgB6SjT76F1NKQLldaS/iutCj23LQzs+Vr4fCtitl14GGEFif+VJGBg7uZ2muZGYtNPrVkwYFWvAFgSA4QsXboE2mFNfa+KKO98sM2jDv7HJRY5NekG9OH2jW7gbQ8OWyjm2ybE5igHb/ZMRbo5gINnTHoLQ9W5L6ep9TC81hzT+3G1vWxVfxAAlLLpOZNDsZg0pdqVOkQdDawJ3hsC+1rBRO3lOetgT1h7Pe8DHZ9SJlnGmHJKwKsrpuxFSfRMFVdx3cETWscomGLbGnesE337iCHrofV6+lbZob7hvqvyHaTqN0o0Jj Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Oct 12, 2026 at 10:29:17AM +0800, Vernon Yang wrote: > From: Vernon Yang > > 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 similar scenarios (e.g. > senpai) will continue to occur, only this time it is for the > /sys/devices/system/nodeX/reclaim knob. > > 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 > > [1] https://github.com/vernon2gh/app_and_module/tree/main/reclaim_node_psi > > Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface") > Cc: stable@vger.kernel.org > Signed-off-by: Vernon Yang Acked-by: Shakeel Butt