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

[Michal Hocko]

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.
-- 
Michal Hocko
SUSE Labs