Re: [PATCH] mm: vmscan: don't count per-node proactive reclaim as memory pressure

[Andrew Morton]

On Mon,  5 Oct 2026 14:22:36 +0800 Vernon Yang <vernon2gm@xxxxxxxxx> 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