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Tue, 26 Sep 2023 01:23:26 -0700 (PDT) MIME-Version: 1.0 References: <20230902100728.3850149-1-liushixin2@huawei.com> In-Reply-To: From: Yosry Ahmed Date: Tue, 26 Sep 2023 01:22:47 -0700 Message-ID: Subject: Re: [PATCH] mm, memcg: expose swapcache stat for memcg v1 To: Christoph Hellwig Cc: Liu Shixin , Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Kefeng Wang , Andrew Morton , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: D5C1B8000D X-Rspam-User: X-Stat-Signature: rddcaj9bg4jdg5tt3x93ttpxmbn6ryt6 X-Rspamd-Server: rspam01 X-HE-Tag: 1695716607-930417 X-HE-Meta: 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 j6Jp14I3 lAgde5XQMTojOG8G10VNX18rNBevUkzDC6Uh5RZGJ23t4BrJFreuJCxhi1Cf+ku5GcvNDMdl4y70P0f84Fq8gISQ1Zzn025NSYvuaMqjRm/Sj+/EJEFZxQjf0WQp/YOUjV6aEUVGBnGChZPdA4EZ+TN5Q9uWBPIQZeYWeQ6HDSHJHzco2gNqhlYXIYDdC8cCRWU1L2D0EoYwOU7v9tixCuPDfm5/P3kDbMy/vquHneeIhLaPYZ6naXSjjLSeESrv9QCs7Zecr1fS8zEHs2WxlsOU27/jBy/zO252vioPr8bcB8U8yNMwHxA0evSNanME6B3rGlR2XgCMnBTC3MpZrBsXfD5LybLBYsdgISLdaBDdEhy4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 26, 2023 at 12:30=E2=80=AFAM Christoph Hellwig wrote: > > On Sat, Sep 02, 2023 at 06:07:28PM +0800, Liu Shixin wrote: > > Since commit b6038942480e ("mm: memcg: add swapcache stat for memcg v2"= ) > > adds swapcache stat for the cgroup v2, it seems there is no reason to > > hide it in memcg v1. Conversely, with swapcached it is more accurate to > > evaluate the available memory for memcg. > > Why are we adding new features to the long deprecated cgroup v1? > Technically this is not a new feature, we are just exposing a stat that the kernel is already tracking (for both cgroup v1 and v2). The reason I suggested to expose this for cgroup v1 is because a recent series [1] started using this stat in the kernel to make some reclaim decisions, for both cgroup v1 and v2. Exposing the stat in v1 will make sure no one assumes the stat is only useful for v2 and break the tracking for v1 (which might cause some reclaim regressions then). [1]https://lore.kernel.org/lkml/20230915083417.3190512-1-liushixin2@huawei.= com/