Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
MIME-Version: 1.0
References: <20231119194740.94101-1-ryncsn@gmail.com> <CAJD7tkYXcQkTZkUnAz89dR0O1YmEUr29UFeg3142t6Y09aaSpg@mail.gmail.com>
In-Reply-To: <CAJD7tkYXcQkTZkUnAz89dR0O1YmEUr29UFeg3142t6Y09aaSpg@mail.gmail.com>
From:   Kairui Song <ryncsn@gmail.com>
Date:   Wed, 22 Nov 2023 14:43:02 +0800
Message-ID: <CAMgjq7DgHvcU6gTWhzPY8By8DCx5TzYViKaiuSSxh-zofuV1HQ@mail.gmail.com>
Subject: Re: [PATCH 00/24] Swapin path refactor for optimization and bugfix
To:     Yosry Ahmed <yosryahmed@google.com>
Cc:     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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Yosry Ahmed <yosryahmed@google.com> =E4=BA=8E2023=E5=B9=B411=E6=9C=8821=E6=
=97=A5=E5=91=A8=E4=BA=8C 03:18=E5=86=99=E9=81=93=EF=BC=9A
>
> On Sun, Nov 19, 2023 at 11:48=E2=80=AFAM Kairui Song <ryncsn@gmail.com> w=
rote:
> >
> > 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 process
> >    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 cgroup=
 B.
> >
>
> I guess this only works for anonymous memory and not shmem, right?

Hi Yosry,

Yes, this patch only changed the charge target for anon page.

>
> 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.

After discuss with others I also found this is a controversial issue,
will send separate series for this, I think it needs more discuss.