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Mon, 14 Aug 2023 17:31:48 -0700 (PDT) MIME-Version: 1.0 References: <20230706062045.xwmwns7cm4fxd7iu@google.com> In-Reply-To: From: Yosry Ahmed Date: Mon, 14 Aug 2023 17:31:12 -0700 Message-ID: Subject: Re: Expensive memory.stat + cpu.stat reads To: Ivan Babrou Cc: Tejun Heo , Waiman Long , Shakeel Butt , cgroups@vger.kernel.org, Linux MM , kernel-team , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , linux-kernel Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 18BD94000B X-Stat-Signature: 6dawrw9pbzwnom3ipca3p5y7133uudfz X-HE-Tag: 1692059509-360033 X-HE-Meta: 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 T7GnKicO RC8/+bi82AvwFPKiK1FN0xIv2EuSlpH9TYK4YtjsbbXXTj8gScVX72CR25noG7V7dgmPyIldqOCR7yWbPbE0UOnJeYuG1I8VO80Nk/zQI83dOuMmyrdaMef7K7QIdO7Yh77fP8Xz51VPz0G3t/8zhf1Nk73vvIiYxI9cWH5B4/SCjItCkVOvbhXVFu31N0dARmviVIFi9XnukwySaxYLJrY4ohX0O/bqWZtqw0zrOl6A2p9NHB+cK95KsIKoUjeLjK+ehh0GtEcKiPwTvoK+YdsqxO0dSjayQKkb5pqtPA6WgeOclExgwmQORPUca677iLD4e67vI5K+yRIE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 14, 2023 at 5:30=E2=80=AFPM Ivan Babrou w= rote: > > On Mon, Aug 14, 2023 at 5:18=E2=80=AFPM Tejun Heo wrote: > > > > Hello, > > > > On Fri, Aug 11, 2023 at 05:01:08PM -0700, Yosry Ahmed wrote: > > > There have been a lot of problems coming from this global rstat lock: > > > hard lockups (when we used to flush atomically), unified flushing > > > being expensive, skipping flushing being inaccurate, etc. > > > > > > I wonder if it's time to rethink this lock and break it down into > > > granular locks. Perhaps a per-cgroup lock, and develop a locking > > > scheme where you always lock a parent then a child, then flush the > > > child and unlock it and move to the next child, etc. This will allow > > > concurrent flushing of non-root cgroups. Even when flushing the root, > > > if we flush all its children first without locking the root, then onl= y > > > lock the root when flushing the top-level children, then some level o= f > > > concurrency can be achieved. > > > > > > Maybe this is too complicated, I never tried to implement it, but I > > > have been bouncing around this idea in my head for a while now. > > > > > > We can also split the update tree per controller. As far as I can tel= l > > > there is no reason to flush cpu stats for example when someone wants > > > to read memory stats. > > > > There's another thread. Let's continue there but I'm a bit skeptical wh= ether > > splitting the lock is a good solution here. Regardless of locking, we d= on't > > want to run in an atomic context for that long anwyay. > > Could you link to the other thread? I supposedly CC'd you there, but I realized it didn't work for some reason: https://lore.kernel.org/lkml/CAJD7tkYBFz-gZ2QsHxUMT=3Dt0KNXs66S-zzMPebadHx9= zaG0Q3w@mail.gmail.com/