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Wed, 26 Jul 2023 08:24:04 -0700 (PDT) MIME-Version: 1.0 References: <20230726002904.655377-1-yosryahmed@google.com> <20230726002904.655377-2-yosryahmed@google.com> <20230726152055.GC1365610@cmpxchg.org> In-Reply-To: <20230726152055.GC1365610@cmpxchg.org> From: Yosry Ahmed Date: Wed, 26 Jul 2023 08:23:28 -0700 Message-ID: Subject: Re: [PATCH v2] mm: memcg: use rstat for non-hierarchical stats To: Johannes Weiner Cc: Roman Gushchin , Michal Hocko , Shakeel Butt , Muchun Song , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: EE55220016 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: hizcuxm9yrz3bkpo96poshhsfjcwje3j X-HE-Tag: 1690385046-454750 X-HE-Meta: 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 n74tduoH TVl5M1oWKGRiu3hWh4TOB6lkiNzhQ32la2i4TMPoAr84sliwAODb79pvP7eW2Sl4aWHdR516Ae4xDQupj0Ez2Qhu6MQEAiE1dMggdjR4A5sAWLVtfV2wRnzCDuwhoz1KzsSs4wpFveP31VDp88UKDUO80F7/Jt+2wn89T2IM9rVXj2LIY3kbd6z61wRT+c3Z4lSZO3w5V9ccGqpTAACPnsgTV/A4ozqG5mXzlmM3vkSjivzRKz2JL7EKgK9XUJaGjIZRlOc20yAwTrjgVpBkTWsc0bb7YDJpnmN2l 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 Wed, Jul 26, 2023 at 8:20=E2=80=AFAM Johannes Weiner wrote: > > On Tue, Jul 25, 2023 at 07:20:02PM -0700, Yosry Ahmed wrote: > > On Tue, Jul 25, 2023 at 7:15=E2=80=AFPM Roman Gushchin wrote: > > > > > > On Wed, Jul 26, 2023 at 12:29:04AM +0000, Yosry Ahmed wrote: > > > > Currently, memcg uses rstat to maintain hierarchical stats. Counter= s 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, t= he > > > 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." Rephrasing sounds good to me. I will send a v3 with the correct commit log and collected Acks to make Andrew's life easier.