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Wed, 14 Oct 2026 02:48:29 +0000 X-Mizu-Trace-ID: e25af03395e5a192 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 14 Oct 2026 10:48:19 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: vmscan: don't count per-node proactive reclaim as memory pressure To: Vernon Yang , akpm@linux-foundation.org, 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 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang , stable@vger.kernel.org References: <20261012022917.1102467-1-vernon2gm@gmail.com> From: Ridong Chen In-Reply-To: <20261012022917.1102467-1-vernon2gm@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 76zx3xqbrnm3prdz857yb7z78nusu5f7 X-Rspamd-Queue-Id: EECD4160005 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1791946110-362699 X-HE-Meta: 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 rYtZ+Gd4 GroLY1cXzVex1gUq7NBz0EhdosFGQz9q0cpgqSpklK5ccO0qs4EM/uA+X1GosK6NjwFNjBFX8KvqyeCwtb+fu4yZzgUregcubtvrzFQQdmBrAehvrB8r67QNAv8KMkmWQFntEposNtn6F671F1zI9hDE640NHYLBx49v1iics8Cm6cQESB5YF+9AgXar4Bih+gndop/OdnOVPE6a25CKYkCpJFS3lx0rkTJrt6tsuchv8mtBP7K5dwFKJF6tK9eEN3dWW9i6x088lhGSrbHFWQBNEUWenGpjNGcnWkr1ZkN0NQD5I3Ig9GQR8CunC4XkINvkOkgviotjBlsPpKz+/lYvP2bPk3JyeQk3I Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/12/2026 10:29 AM, 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 > --- > V1 -> V2: > - Check `sc->proactive` to differentiate between proactive reclaim or > page allocation. (Thanks Barry) > > V1 : https://lore.kernel.org/linux-mm/20261005062236.564210-1-vernon2gm@gmail.com/ > --- > mm/vmscan.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 91295070ca33..2e9ca5e4c741 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -7994,7 +7994,8 @@ static unsigned long __node_reclaim(struct pglist_data *pgdat, > sc->gfp_mask); > > cond_resched(); > - psi_memstall_enter(&pflags); > + if (!sc->proactive) > + psi_memstall_enter(&pflags); > delayacct_freepages_start(); > fs_reclaim_acquire(sc->gfp_mask); > /* > @@ -8011,7 +8012,8 @@ static unsigned long __node_reclaim(struct pglist_data *pgdat, > memalloc_noreclaim_restore(noreclaim_flag); > fs_reclaim_release(sc->gfp_mask); > delayacct_freepages_end(); > - psi_memstall_leave(&pflags); > + if (!sc->proactive) > + psi_memstall_leave(&pflags); > > trace_mm_vmscan_node_reclaim_end(sc->nr_reclaimed, NULL); > LGTM. Reviewed-by: Ridong Chen Thanks. -- Best regards Ridong