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Wed, 26 Jul 2023 08:20:57 -0700 (PDT) Received: from localhost ([2620:10d:c091:400::5:ad06]) by smtp.gmail.com with ESMTPSA id g12-20020ae9e10c000000b00767291640e8sm4424608qkm.90.2023.07.26.08.20.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jul 2023 08:20:56 -0700 (PDT) Date: Wed, 26 Jul 2023 11:20:55 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Roman Gushchin , Michal Hocko , Shakeel Butt , Muchun Song , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm: memcg: use rstat for non-hierarchical stats Message-ID: <20230726152055.GC1365610@cmpxchg.org> References: <20230726002904.655377-1-yosryahmed@google.com> <20230726002904.655377-2-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 1E978160025 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ftu6zcftx3bnwqsjrrfdhj6h8ku3f8ze X-HE-Tag: 1690384857-778802 X-HE-Meta: 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 tisAN1iD aJPpzmzBm/DPIH4SKkv050jieLKyBHRqEW86aoHGQOEYk3pUG7WGBykmXzZsrVfvonXHKRoVd0YaI5d6y7N85ZxV75f233/VQzuZUVkse3bLrah46aTkH+A3A9RxRpJEQgfmIhtcPlBxtZ4QBMpULJuiU4SCBnUkS0qiwVLDKZulzhJeI2u1h1LOwsvOl9Mny1wuLaGgSF+YhOB/qlb5vWF7FRBAIhlR0pegWXA6RF7RXEsIebBa81P4t0owUk3OSAOWd7BxLx79L+tnK5LgjzLUGMChTKvUmrhNASCS+e8A4/qv5OZcMsAU5tkiO+oZs4FkGW7CS6SpppaNePZrM1b0/uRwlU/PY4vV7V7l5eYzecPDutvGF/q/Rv7DpEbuLYcR+jPAXRBqCcbnI+/xt2UvSIlHcF+Vx4ylqJU4pnfOPh30= 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 Tue, Jul 25, 2023 at 07:20:02PM -0700, Yosry Ahmed wrote: > On Tue, Jul 25, 2023 at 7:15 PM Roman Gushchin wrote: > > > > On Wed, Jul 26, 2023 at 12:29:04AM +0000, Yosry Ahmed wrote: > > > Currently, memcg uses rstat to maintain hierarchical stats. Counters are > > > maintained for hierarchical stats at each memcg. Rstat tracks which > > > cgroups have updates on which cpus to keep those counters fresh on the > > > read-side. > > > > > > For non-hierarchical stats, we do not maintain counters. Instead, the > > global? > > Do you mean "we do not maintain global counters"? I think "global" is > confusing, because it can be thought of as all cpus or as including > the subtree (as opposed to local for non-hierarchical stats). "global" seems fine to me, I don't think it's ambiguous in the direct comparison with per-cpu counts. Alternatively, rephrase the whole thing? Something like: "Non-hierarchical stats are currently not covered by rstat. Their per-cpu counters are summed up on every read, which is expensive."