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From: Chris Li <chrisl@kernel.org>
Date: Thu, 14 Dec 2023 15:22:27 -0800
Message-ID: <CAF8kJuMLDOaP6-Xyz-+hzLbDuYW7gfG9jA06j6t5v7XX2rPOdw@mail.gmail.com>
Subject: Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling
To: Fabian Deutsch <fdeutsch@redhat.com>
Cc: Yu Zhao <yuzhao@google.com>, Johannes Weiner <hannes@cmpxchg.org>, 
	Minchan Kim <minchan@kernel.org>, Nhat Pham <nphamcs@gmail.com>, akpm@linux-foundation.org, 
	tj@kernel.org, lizefan.x@bytedance.com, cerasuolodomenico@gmail.com, 
	yosryahmed@google.com, sjenning@redhat.com, ddstreet@ieee.org, 
	vitaly.wool@konsulko.com, mhocko@kernel.org, roman.gushchin@linux.dev, 
	shakeelb@google.com, muchun.song@linux.dev, hughd@google.com, corbet@lwn.net, 
	konrad.wilk@oracle.com, senozhatsky@chromium.org, rppt@kernel.org, 
	linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, 
	linux-doc@vger.kernel.org, david@ixit.cz, Kairui Song <kasong@tencent.com>, 
	Zhongkun He <hezhongkun.hzk@bytedance.com>
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Hi Fabian,

On Thu, Dec 14, 2023 at 10:00=E2=80=AFAM Fabian Deutsch <fdeutsch@redhat.co=
m> wrote:

> Yep - for container use-cases.
>
> Now a few thoughts in this direction:
> - With swap per cgroup you loose the big "statistical" benefit of having =
swap on a node level. well, it depends on the size of the cgroup (i.e. syst=
em.slice is quite large).

Just to clarify, the "node" you mean the "node" in kubernetes sense,
which is the whole machine. In the Linux kernel MM context, the node
often refers to the NUMA memory node, that is not what you mean here,
right?

> - With todays node level swap, and setting memory.swap.max=3D0 for all cg=
roups allows you toachieve a similar behavior (only opt-in cgroups will get=
 swap).
> - the above approach however will still have a shared swap backend for al=
l cgroups.

Yes, the "memory.swap.tires" idea is trying to allow cgroups to select
a subset of the swap backend in a specific order. It is still in the
early stage of discussion. If you have any suggestion or feedback in
that direction, I am looking forward to hearing that.

Chris