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Mon, 11 Sep 2023 12:15:36 -0700 (PDT) MIME-Version: 1.0 References: <20230831165611.2610118-1-yosryahmed@google.com> <20230831165611.2610118-5-yosryahmed@google.com> In-Reply-To: From: Wei Xu Date: Mon, 11 Sep 2023 12:15:24 -0700 Message-ID: Subject: Re: [PATCH v4 4/4] mm: memcg: use non-unified stats flushing for userspace reads To: Michal Hocko Cc: Yosry Ahmed , Andrew Morton , Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Ivan Babrou , Tejun Heo , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Waiman Long , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Thelen Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 5F6B080009 X-Rspam-User: X-Stat-Signature: j38sekfbw7datj1mscgt6gwc5ec65i6x X-Rspamd-Server: rspam03 X-HE-Tag: 1694459738-693495 X-HE-Meta: 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 +4Xz0wUb Yc9RFDIGznhSy8vY8oQS6jXDkYVhXLor1P863GsDTcDBbwHbMVylC9XL2NL3tLeNZRbd0rhQxMzICfxZhce7mU6MC2aZnCvyLrc+jBhQ4+iaJQGcxM5e2Z2SNkKt4ei7LDK0OsUv6/LKCM8zcMxgUDdzunsMAlYfEZ2txmsQjdwWWUK+Qn2sD2fO29YEuBOPYWwySDTRux7TUdQE9SpEMfvPHTO4VfxuiGj56i1Xp2KKVcwFOQDLfuTcUk4uowft3ql+MRuZWGqelr/GYkUqEff2HmW0tr6PDwEOn 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, Sep 11, 2023 at 6:11=E2=80=AFAM Michal Hocko wrot= e: > > On Thu 07-09-23 17:52:12, Wei Xu wrote: > [...] > > I tested this patch on a machine with 384 CPUs using a microbenchmark > > that spawns 10K threads, each reading its memory.stat every 100 > > milliseconds. > > This is rather extreme case but I wouldn't call it utterly insane > though. > > > Most of memory.stat reads take 5ms-10ms in kernel, with > > ~5% reads even exceeding 1 second. > > Just curious, what would numbers look like if the mutex is removed and > those threads would be condending on the existing spinlock with lock > dropping in place and removed. Would you be willing to give it a shot? Without the mutex and with the spinlock only, the common read latency of memory.stat is still 5ms-10ms in kernel. There are very few reads (<0.003%) going above 10ms and none more than 1 second. > -- > Michal Hocko > SUSE Labs