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From:   Kairui Song <ryncsn@gmail.com>
Date:   Wed, 22 Nov 2023 14:46:13 +0800
Message-ID: <CAMgjq7CyRa9Sz7ri+L0Nz=GVOqFtyWt6dKont0Kvks6K5Ei45g@mail.gmail.com>
Subject: Re: [PATCH 00/24] Swapin path refactor for optimization and bugfix
To:     Chris Li <chrisl@kernel.org>
Cc:     Yosry Ahmed <yosryahmed@google.com>, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        "Huang, Ying" <ying.huang@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@suse.com>, linux-kernel@vger.kernel.org
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Chris Li <chrisl@kernel.org> =E4=BA=8E2023=E5=B9=B411=E6=9C=8821=E6=97=A5=
=E5=91=A8=E4=BA=8C 04:23=E5=86=99=E9=81=93=EF=BC=9A
>
> Hi Kairui,
>
> On Mon, Nov 20, 2023 at 11:10=E2=80=AFAM Yosry Ahmed <yosryahmed@google.c=
om> wrote:
> >
> > On Sun, Nov 19, 2023 at 11:48=E2=80=AFAM Kairui Song <ryncsn@gmail.com>=
 wrote:
> > >
> > > From: Kairui Song <kasong@tencent.com>
> > >
> > > This series tries to unify and clean up the swapin path, fixing a few
> > > issues with optimizations:
> > >
> > > 1. Memcg leak issue: when a process that previously swapped out some
> > >    migrated to another cgroup, and the origianl cgroup is dead. If we
> > >    do a swapoff, swapped in pages will be accounted into the process
> > >    doing swapoff instead of the new cgroup. This will allow the proce=
ss
> > >    to use more memory than expect easily.
> > >
> > >    This can be easily reproduced by:
> > >    - Setup a swap.
> > >    - Create memory cgroup A, B and C.
> > >    - Spawn process P1 in cgroup A and make it swap out some pages.
> > >    - Move process P1 to memory cgroup B.
> > >    - Destroy cgroup A.
> > >    - Do a swapoff in cgroup C
> > >    - Swapped in pages is accounted into cgroup C.
> > >
> > >    This patch will fix it make the swapped in pages accounted in cgro=
up B.
> > >
> >
> > I guess this only works for anonymous memory and not shmem, right?
> >
> > I think tying memcg charges to a process is not something we usually
> > do. Charging the pages to the memcg of the faulting process if the
> > previous owner is dead makes sense, it's essentially recharging the
> > memory to the new owner. Swapoff is indeed a special case, since the
> > faulting process is not the new owner, but an admin process or so. I
> > am guessing charging to the new memcg of the previous owner might make
> > sense in this case, but it is a change of behavior.
> >
>
> I was looking at this at patch 23 as well. Will ask more questions in
> the patch thread.
> I would suggest making these two behavior change patches separate out
> from the clean up series to give it more exposure and proper
> discussion.
> Patch 5 and patch 23.
>
> Chris
>

Hi Chris,

Thank you very much for reviewing these details, it's really helpful.

I'll send out new serieses after checking your suggestions on these patches=
.