Re: [PATCH v1] mm/vmscan: mitigate spurious kswapd_failures reset from direct reclaim

[Jiayuan Chen]

January 6, 2026 at 17:49, "Michal Hocko" <mhocko@xxxxxxxx mailto:mhocko@xxxxxxxx?to=%22Michal%20Hocko%22%20%3Cmhocko%40suse.com%3E > wrote:


> 
> On Tue 06-01-26 05:25:42, Jiayuan Chen wrote:
> 
> > 
> > That said, I believe this patch is still a valid fix on its own - resetting kswapd_failures
> >  when the node is not actually balanced doesn't seem like correct behavior regardless of the
> >  broader context.
> > 
> Originally I was more inclined to opt out memcg reclaim from reseting
> kswapd retry counter but the more I am thiking about that the more your
> patch makes sense to me. 
> 
> The reason being that it handles both memcg and global direct reclaims
> in the same way which makes the logic easier to follow. Afterall the
> primary purpose is to resurrect kswapd after we can see there is a
> better chance to reclaim something for kswapd. Until that moment direct
> reclaim is the only reclaim mechanism.
> 
> Relying on pgdat_balanced might lead to re-enabling kswapd way much
> later while memory reclaim would be still mostly direct reclaim bound -
> thus increase allocation latencies.
> If we wanted to do better we would need to evaluate recent
> refaults/thrashing behavior but even then I am not sure we can make a
> good cut off.
> 
> So in the end pgdat_balanced approach seems worth trying and see whether
> this could cause any corner cases.

Thanks Michal.

Regarding the allocation latency concern - we are already
in the direct reclaim slowpath, so a little extra overhead
from the pgdat_balanced check should be negligible.

> -- 
> Michal Hocko
> SUSE Labs
>