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[2003:d8:2f0a:7f00:fad7:3bc9:69d:31f]) by smtp.gmail.com with ESMTPSA id z2sm5312534wma.45.2021.07.28.01.21.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Jul 2021 01:21:19 -0700 (PDT) Subject: Re: [PATCH] memcg: cleanup racy sum avoidance code To: Shakeel Butt , Michal Hocko , Johannes Weiner , Roman Gushchin Cc: Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210728012243.3369123-1-shakeelb@google.com> From: David Hildenbrand Organization: Red Hat Message-ID: <8c35e469-b355-63b0-6cd4-ca39c39ddb79@redhat.com> Date: Wed, 28 Jul 2021 10:21:18 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210728012243.3369123-1-shakeelb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BC85C70148F1 Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="fiF/vVqd"; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf27.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com X-Stat-Signature: 7cmgry4z8mo94earfjuo6zj75crjgrc8 X-HE-Tag: 1627460482-475830 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 28.07.21 03:22, Shakeel Butt wrote: > We used to have per-cpu memcg and lruvec stats and the readers have to > traverse and sum the stats from each cpu. This summing was racy and may > expose transient negative values. So, an explicit check was added to > avoid such scenarios. Now these stats are moved to rstat infrastructure > and are no more per-cpu, so we can remove the fixup for transient > negative values. > > Signed-off-by: Shakeel Butt > --- > include/linux/memcontrol.h | 15 ++------------- > 1 file changed, 2 insertions(+), 13 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 7028d8e4a3d7..5f2a39a43d47 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -991,30 +991,19 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg, > > static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx) > { > - long x = READ_ONCE(memcg->vmstats.state[idx]); > -#ifdef CONFIG_SMP > - if (x < 0) > - x = 0; > -#endif > - return x; > + return READ_ONCE(memcg->vmstats.state[idx]); > } > > static inline unsigned long lruvec_page_state(struct lruvec *lruvec, > enum node_stat_item idx) > { > struct mem_cgroup_per_node *pn; > - long x; > > if (mem_cgroup_disabled()) > return node_page_state(lruvec_pgdat(lruvec), idx); > > pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); > - x = READ_ONCE(pn->lruvec_stats.state[idx]); > -#ifdef CONFIG_SMP > - if (x < 0) > - x = 0; > -#endif > - return x; > + return READ_ONCE(pn->lruvec_stats.state[idx]); > } > > static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec, > Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb