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Tue, 28 Mar 2023 11:47:47 -0700 (PDT) Date: Tue, 28 Mar 2023 14:47:46 -0400 From: Johannes Weiner To: Shakeel Butt Cc: Yosry Ahmed , Tejun Heo , Josef Bacik , Jens Axboe , Zefan Li , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , Michal =?iso-8859-1?Q?Koutn=FD?= , Vasily Averin , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org Subject: Re: [PATCH v1 7/9] workingset: memcg: sleep when flushing stats in workingset_refault() Message-ID: References: <20230328061638.203420-1-yosryahmed@google.com> <20230328061638.203420-8-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 162F3140005 X-Stat-Signature: 5hb8rnxwiqmsqfc6ghq8ma9fheyki798 X-Rspam-User: X-HE-Tag: 1680029268-533125 X-HE-Meta: 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 R9084uxR 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 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, Mar 28, 2023 at 08:18:11AM -0700, Shakeel Butt wrote: > > @@ -406,6 +406,8 @@ void workingset_refault(struct folio *folio, void *shadow) > > unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset); > > eviction <<= bucket_order; > > > > + /* Flush stats (and potentially sleep) before holding RCU read lock */ > > I think the only reason we use rcu lock is due to > mem_cgroup_from_id(). Maybe we should add mem_cgroup_tryget_from_id(). > The other caller of mem_cgroup_from_id() in vmscan is already doing > the same and could use mem_cgroup_tryget_from_id(). Good catch. Nothing else in there is protected by RCU. We can just hold the ref instead. > Though this can be done separately to this series (if we decide to do > it at all). Agreed