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

[Barry Song]

On Mon, Oct 5, 2026 at 2:23 PM Vernon Yang <vernon2gm@xxxxxxxxx> wrote:
>
> From: Vernon Yang <yanglincheng@xxxxxxxxxx>
>
> 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.
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Vernon Yang <yanglincheng@xxxxxxxxxx>
> ---

This seems to be a valid concern. Personally, I don't like
having the code depend on whether `__node_reclaim()` and
`node_reclaim()` are called from proactive reclaim or page
allocation.

Can't we check whether `sc->proactive` is true? Am I missing
something?

Best Regards
Barry