Re: [External] Re: [PATCH] mm: vmscan: skip the file folios in proactive reclaim if swappiness is MAX

[Zhongkun He <hezhongkun.hzk@bytedance.com>]

On Fri, Mar 14, 2025 at 8:17 AM Yosry Ahmed <yosry.ahmed@linux.dev> wrote:
>
> On Wed, Mar 12, 2025 at 05:43:37PM +0800, Zhongkun He wrote:
> > With this patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
> > memory.reclaim")', we can submit an additional swappiness=<val> argument
> > to memory.reclaim. It is very useful because we can dynamically adjust
> > the reclamation ratio based on the anonymous folios and file folios of
> > each cgroup. For example,when swappiness is set to 0, we only reclaim
> > from file pages.
> >
> > However,we have also encountered a new issue: when swappiness is set to
> > the MAX_SWAPPINESS, it may still only reclaim file folios. This is due
> > to the knob of cache_trim_mode, which depends solely on the ratio of
> > inactive folios, regardless of whether there are a large number of cold
> > folios in anonymous folio list.
> >
> > So, we hope to add a new control logic where proactive memory reclaim only
> > reclaims from anonymous folios when swappiness is set to MAX_SWAPPINESS.
> > For example, something like this:
> >
> > echo "2M swappiness=200" > /sys/fs/cgroup/memory.reclaim
> >
> > will perform reclaim on the rootcg with a swappiness setting of 200 (max
> > swappiness) regardless of the file folios. Users have a more comprehensive
> > view of the application's memory distribution because there are many
> > metrics available.
> >
> > With this patch, the swappiness argument of memory.reclaim has a more
> > precise semantics: 0 means reclaiming only from file pages, while 200
> > means reclaiming just from anonymous pages.
> >
> > Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
>
> Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Thanks for your time, Yosry.

>
> > ---
> >  mm/vmscan.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index c767d71c43d7..f4312b41e0e0 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2438,6 +2438,16 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> >               goto out;
> >       }
> >
> > +     /*
> > +      * Do not bother scanning file folios if the memory reclaim
> > +      * invoked by userspace through memory.reclaim and the
> > +      * swappiness is MAX_SWAPPINESS.
> > +      */
> > +     if (sc->proactive && (swappiness == MAX_SWAPPINESS)) {
> > +             scan_balance = SCAN_ANON;
> > +             goto out;
> > +     }
> > +
> >       /*
> >        * Do not apply any pressure balancing cleverness when the
> >        * system is close to OOM, scan both anon and file equally
> > --
> > 2.39.5
> >
> >