Re: [PATCH] mm/vmscan: clear hopeless kswapd when global direct reclaim makes progress

[Andrew Morton <akpm@linux-foundation.org>]

On Thu,  9 Jul 2026 19:44:29 -0700 Altan Hacigumus <ahacigu.linux@gmail.com> wrote:

> Direct reclaim clears the hopeless kswapd state only once the node
> becomes balanced. This avoids cgroup memory.high reclaim repeatedly
> reviving a kswapd that cannot balance the node.
> 
> However, it also prevents global direct reclaim from reviving kswapd.
> Under sustained memory pressure, global direct reclaim may continue
> making progress without the node ever reaching the high watermark,
> leaving reclaim to allocating tasks.
> 
> Unlike memcg reclaim, global direct reclaim follows the same node-wide
> reclaim path as kswapd. Clear the hopeless state when global direct
> reclaim makes progress, while continuing to require a balanced node for
> memcg reclaim. kswapd_try_clear_hopeless() becomes static since struct
> scan_control is private to vmscan.c.
> 
> On a workload with most memory mlocked and the remainder under sustained
> churn, with swap enabled, comparing the same 60s window:
>                               base       patched
>   allocstall (all zones)    413441          6532
>   pgsteal_direct          15889552        255619
>   pgsteal_kswapd                 0      26079382
>   PSI memory full avg60     13.10%         9.37%
> 
> Direct reclaim was already reclaiming many pages in the baseline;
> this change lets kswapd resume doing that work asynchronously.

Does this change have any user-visible effect?  If so, please describe
in elaborate detail.

If not then that's OK - we make such changes all the time, but they're
less fun.