linux-kernel - Re: [PATCH] mm: memcg: export workingset refault stats for cgroup v1

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Date:   Tue, 16 Aug 2022 19:05:19 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: [PATCH] mm: memcg: export workingset refault stats for cgroup v1

On Tue, Aug 16, 2022 at 7:01 PM Yang Shi <shy828301@...il.com> wrote:
>
> On Tue, Aug 16, 2022 at 3:06 PM Shakeel Butt <shakeelb@...gle.com> wrote:
> >
> > On Tue, Aug 16, 2022 at 11:58 AM Yang Shi <shy828301@...il.com> wrote:
> > >
> > > Workingset refault stats are important and usefule metrics to measure
> > > how well reclaimer and swapping work and how healthy the services are,
> > > but they are just available for cgroup v2.  There are still plenty users
> > > with cgroup v1, export the stats for cgroup v1.
> > >
> > > Signed-off-by: Yang Shi <shy828301@...il.com>
> > > ---
> > > I do understand the development of cgroup v1 is actually stalled and
> > > the community is reluctant to accept new features for v1.  However
> > > the workingset refault stats are really quite useful and exporting
> > > two new stats, which have been supported by v2, seems ok IMHO.  So
> > > hopefully this patch could be considered.  Thanks.
> > >
> >
> > Is just workingset refault good enough for your use-case? What about
> > the other workingset stats? I don't have a strong opinion against
> > adding these to v1 and I think these specific stats should be fine.
>
> The workingset refault is good enough for our usercase, but I don't
> mind adding all the workingset_* stats if nobody has objection.

For now let's just start with what your use-case needs. If in future
there is a need we can add other workingset_* stats as well.

>
> > (There is subtlety in exposing objcg based stats (i.e. reparenting) in
> > v1 due to non-hierarchical stats in v1. I remember Yosry and Muchun
> > were looking into that.)
>
> The workingset_* stats should have nothing to do with obj based stats IIUC.

Yeah, that was just FYI for anyone in future who wants to export such
stat in v1.