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Wed, 26 Jul 2023 08:13:16 -0700 (PDT) Received: from localhost ([2620:10d:c091:400::5:ad06]) by smtp.gmail.com with ESMTPSA id a26-20020a0c8bda000000b006238b37fb05sm283391qvc.119.2023.07.26.08.13.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jul 2023 08:13:16 -0700 (PDT) Date: Wed, 26 Jul 2023 11:13:15 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: linux-kernel@vger.kernel.org, Michal Hocko , cgroups@vger.kernel.org, linux-mm@kvack.org, Muchun Song , Shakeel Butt , Roman Gushchin , Andrew Morton Subject: Re: [PATCH v2] mm: memcg: use rstat for non-hierarchical stats Message-ID: <20230726151315.GB1365610@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-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 99D8E14000B X-Stat-Signature: ne3diu8tpoe7dew1n6kjy5x95wwykifd X-HE-Tag: 1690384397-828535 X-HE-Meta: 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 hFsyPKCG zlYc5rcWEZD9LtOjxDvgKrfIqaCXQi2Y+RZJpFbS2sBaRw/DR8beTspPbv8l5Gq5v59bbsCIlKfAeXIZhdn+55u3LFDSKNC9tJrQmPNY5pkCBtFqc5978FFUxAzShIu/LAFRN5DBlzoa7jWZqYpV5VX9IaU4dTX+9PBZpZYf/wBBx/Q355fThbNNgeYC5sS42Ci5ytbmL2JyKIzYeNCi8HoKFhfU8XoNXqtCCup+pXUWtzxuEEf2Op1hAbl73TXRzUPWRdlSiX0VECo2YLwpnFuCT1Dt+4ezebIIIvqDieRJQoXFsHAPEHFlQ2OFvoB6Ki4DWwEnYW1A1tLwrKF2OH/8IBflh0BZGHBx0To8fBheDRXF3ssX/V97Q/PqFUyVNb0k7fBaT/YobdrunN1WF66l1k/j635Vr4tinDQFVpoVG+9vEtbWjGtkjROBA//3DV2MK 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 05:36:45PM -0700, Yosry Ahmed wrote: > On Tue, Jul 25, 2023 at 5:29 PM Yosry Ahmed wrote: > > - Fix a subtle bug where updating a local counter would be missed if it > > was cancelled out by a pending update from child memcgs. > > > Johannes, I fixed a subtle bug here and I kept your Ack, I wasn't sure > what the Ack retention policy should be here. A quick look at the fix > would be great. Ah, I found it: > > @@ -5542,19 +5539,23 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu) > > memcg->vmstats->state_pending[i] = 0; > > > > /* Add CPU changes on this level since the last flush */ > > + delta_cpu = 0; > > v = READ_ONCE(statc->state[i]); > > if (v != statc->state_prev[i]) { > > - delta += v - statc->state_prev[i]; > > + delta_cpu = v - statc->state_prev[i]; > > + delta += delta_cpu; > > statc->state_prev[i] = v; > > } > > > > - if (!delta) > > - continue; > > - > > /* Aggregate counts on this level and propagate upwards */ > > - memcg->vmstats->state[i] += delta; > > - if (parent) > > - parent->vmstats->state_pending[i] += delta; > > + if (delta_cpu) > > + memcg->vmstats->state_local[i] += delta_cpu; When delta nulls out, but delta_cpu is non-zero... subtle. This fixed version looks good, please keep my ack :)