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From:   "T.J. Mercier" <tjmercier@google.com>
Date:   Wed, 18 Oct 2023 12:59:07 -0700
Message-ID: <CABdmKX0xevnJfcgsDEWsfX9J5T2x0EV7x-p4ommq_Deg98WwYA@mail.gmail.com>
Subject: Re: [PATCH 0/3 RESEND] Per memcg lru_gen node stat
To:     Yu Zhao <yuzhao@google.com>
Cc:     Huan Yang <link@vivo.com>, Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Peter Xu <peterx@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        "T.J. Alumbaugh" <talumbau@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Suren Baghdasaryan <surenb@google.com>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <cgroups@vger.kernel.org>, opensource.kernel@vivo.com
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On Wed, Oct 18, 2023 at 9:34=E2=80=AFAM Yu Zhao <yuzhao@google.com> wrote:
>
> On Sun, Oct 8, 2023 at 8:57=E2=80=AFPM Huan Yang <link@vivo.com> wrote:
> >
> > On original global lru_gen node in debugfs, it can all show each memcg'=
s
> > lru gen info in "lru_gen" or "lru_gen_full", and can type cmd into lru_=
gen.
> > But which show info contains all memcg's info, and cmd need to
> > know memcg's id.
> >
> > This patchset add lru_gen node in per memcg, with this node, we can
> > get lru_gen info in each memcg.
> > Also, we can type cmd to control each memcg's lru_gen seq, but, this no=
de
> > don't support multi cmd, single memcg just process one cmd once time.
>
> Adding TJ from the Android team. (The other TJ you CC'ed is from the
> ChromeOS team.)
>
> This series introduced a new ABI, which has to be maintained forever.
> How exactly would it be used in *production*?
>
> Android doesn't officially support memcgs. So I want to understand the
> real-world use cases first.

Not sure how Android came up but I'm happy to chat. We want to turn on
memcg v2 for Android but I'm currently working through perf impacts
before that happens. Android can't use debugfs in production, but I
think we'd prefer to use memory.reclaim for eviction anyway because it
respects memcg limits and reclaims from slab.

So maybe it's possible to add just aging functionality specific to
MGLRU? It'd be nice to know how you're going to use the aging, or why
you want this version of eviction instead of what memory.reclaim does.