Re: [PATCH v5 1/6] mm/zswap: Fix global shrinker when memory cgroup is disabled

[Hao Jia]

On 2026/7/1 00:02, Yosry Ahmed wrote:
> > How about something like this? If there are no objections, I'll fold
> > this into the next version.
> >
> >       mm/zswap: Fix global shrinker when memory cgroup is disabled
> >
> >       When memory cgroup is disabled, mem_cgroup_iter() always returns NULL.
> >       Therefore, the global shrinker shrink_worker() always takes the !memcg
> >       branch. After MAX_RECLAIM_RETRIES empty walks, the worker simply
> > gives up,
> >       so it fails to write back anything.
> >
> >       Therefore, when memory cgroup is disabled, fall through with the !memcg
> >       branch and shrink the root memcg directly.
> >
> >       With memcg disabled, shrink_memcg() only returns -ENOENT when the root
> >       LRU is empty, which means the total pages are already below thr.
> > The loop
> >       then safely bails out via the zswap_total_pages() <= thr check. For any
> >       other return value from shrink_memcg(), the loop is guaranteed to
> > terminate,
> >       either after MAX_RECLAIM_RETRIES failures or once the threshold is met.
> >
> >       Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")
> >       Cc: stable@xxxxxxxxxxxxxxx
> >       Reported-by: Yosry Ahmed <yosry@xxxxxxxxxx>
> >       Closes:
> > https://lore.kernel.org/all/CAO9r8zPVzMKFbCixxD-qgtRrkFxWVrHiZZeLc=eyTPKPVQgX4g@xxxxxxxxxxxxxx
> >       Signed-off-by: Hao Jia <jiahao1@xxxxxxxxxxx>
>
> Feel free to add:
>
> Acked-by: Yosry Ahmed <yosry@xxxxxxxxxx>

Thank you for taking the time to review this.
> A small nit below.
>
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 4b5149173b0e..9d4f19fc440e 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -1361,11 +1361,12 @@ static void shrink_worker(struct work_struct *w)
> >                   } while (memcg && !mem_cgroup_tryget_online(memcg));
> >                   spin_unlock(&zswap_shrink_lock);
> >
> > -               if (!memcg) {
> > -                       /*
> > -                        * Continue shrinking without incrementing
> > failures if
> > -                        * we found candidate memcgs in the last tree walk.
> > -                        */
> > +               /*
> > +                * A NULL memcg ends a full hierarchy pass (except when
> > memcg is
> > +                * disabled, where it is always NULL: fall through to
> > the root LRU).
> > +                * Count a failure only if the pass found no candidates.
>
> I think "last pass" is clearer than just "pass" here?


Will do.

Thanks,
Hao