From 2ca8b38962f239b17f7881a4710c11328ce38ac9 Mon Sep 17 00:00:00 2001 From: Vernon Yang Date: Mon, 12 Oct 2026 10:29:17 +0800 Subject: [PATCH] mm: vmscan: don't count per-node proactive reclaim as memory pressure 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 Link: https://lore.kernel.org/20261012022917.1102467-1-vernon2gm@gmail.com Link: https://github.com/vernon2gh/app_and_module/tree/main/reclaim_node_psi [1] Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface") Signed-off-by: Vernon Yang Signed-off-by: Andrew Morton Reviewed-by: Baolin Wang Reviewed-by: Barry Song Reviewed-by: Ridong Chen Acked-by: Davidlohr Bueso Cc: David Hildenbrand Cc: Kairui Song Cc: Qi Zheng Cc: Shakeel Butt Cc: Axel Rasmussen Cc: Yuanchu Xie Cc: Wei Xu Cc: Baoquan He Cc: Johannes Weiner Cc: Michal Hocko Cc: Lorenzo Stoakes Cc: Roman Gushchin Cc: --- mm/vmscan.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 28dbc5137e68..daa7e37c2236 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -7998,7 +7998,8 @@ 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); /* @@ -8015,7 +8016,8 @@ 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);