linux-kernel - Re: [PATCH] mm: skip current when memcg reclaim

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Date:   Sat, 16 Oct 2021 10:28:54 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: skip current when memcg reclaim

On Sat, Oct 16, 2021 at 4:00 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@...il.com> wrote:
>
> > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> >
> > Sibling thread of the same process could refault the reclaimed pages
> > in the same time, which would be typical in None global reclaim and
> > introduce thrashing.
>
> "None" -> "node", I assume?
>
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
> >                               sc->memcg_low_skipped = 1;
> >                               continue;
> >                       }
> > +                     /*
> > +                      * Don't bother current when its memcg is below low
> > +                      */
>
> The comment explains what the code is doing, but the code itself
> already does this.  Please can we have a comment that explains *why*
> the code is doing this?
We find that the patch help direct reclaiming bail out early and
eliminate page thrashing for some scenarios(etc APP start on android).
The case could be worse if each APP possess a unique memcg(pages on
current's lru are reclaimed more than global reclaim)
>
>
> > +                     if (get_mem_cgroup_from_mm(current->mm) == memcg)
> > +                             continue;
> >                       memcg_memory_event(memcg, MEMCG_LOW);
> >               }
>