Re: [PATCH] mm: vmscan: abort proactive reclaim early when freezing

[Richard Chang <richardycc@google.com>]

Hi Yosry,

I believe we still need the outer loop check. Otherwise, we will waste
CPU cycles entering the inner loop only to bail out.

On Tue, Jul 7, 2026 at 10:20 AM Yosry Ahmed <yosry@kernel.org> wrote:
>
> On Mon, Jul 06, 2026 at 08:12:18AM +0000, Richard Chang wrote:
> > Proactive reclaim (via memory.reclaim or node reclaim) checks for pending
> > signals in its outer loop in user_proactive_reclaim(). However, the inner
> > reclaim loops—scanning cgroups in shrink_many() and evicting folios in
> > try_to_shrink_lruvec() can run for a long time before returning to the
> > outer loop, especially on systems with many cgroups or large memory sizes.
> >
> > This latency in responding to signals can block the freezer (both cgroup
> > freezer and system suspend), leading to freezer timeouts. This issue was
> > specifically observed on Android when attempting to freeze background
> > cgroups while proactive reclaim was active.
> >
> > Add a signal_pending() check to should_abort_scan() for proactive reclaim
> > paths. Since should_abort_scan() is called within the inner scanning and
> > eviction loops, this allows proactive reclaim to abort early and return to
> > the outer loop, ensuring the task can enter the refrigerator in a timely
> > manner.
>
> Do we still need the check in the outer loop?
>
> >
> > This check is limited to proactive reclaim (sc->proactive) to avoid
> > affecting reactive reclaim paths, and wrapped in unlikely() as it is a
> > slow path.
> >
> > Signed-off-by: Richard Chang <richardycc@google.com>
> > ---
> >  mm/vmscan.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 35c3bb15ae96..fb472e924fc7 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4929,6 +4929,9 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
> >       int i;
> >       enum zone_watermarks mark;
> >
> > +     if (unlikely(sc->proactive && signal_pending(current)))
> > +             return true;
> > +
> >       if (sc->nr_reclaimed >= max(sc->nr_to_reclaim, compact_gap(sc->order)))
> >               return true;
> >
> > --
> > 2.55.0.rc2.803.g1fd1e6609c-goog
> >
> >