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Tue, 28 Mar 2023 12:06:05 -0700 (PDT) Received: from localhost ([2a02:8070:6387:ab20:5139:4abd:1194:8f0e]) by smtp.gmail.com with ESMTPSA id xh9-20020a170906da8900b009447277c26fsm3069805ejb.72.2023.03.28.12.06.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Mar 2023 12:06:05 -0700 (PDT) Date: Tue, 28 Mar 2023 15:06:03 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Tejun Heo , Josef Bacik , Jens Axboe , Zefan Li , Michal Hocko , Roman Gushchin , Shakeel Butt , 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 6/9] memcg: sleep during flushing stats in safe contexts Message-ID: References: <20230328061638.203420-1-yosryahmed@google.com> <20230328061638.203420-7-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: C3C4440013 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: oxknyscwm93u3m37oatnc944jqctez6r X-HE-Tag: 1680030366-497732 X-HE-Meta: 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 RFdCwVaa 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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 11:45:19AM -0700, Yosry Ahmed wrote: > On Tue, Mar 28, 2023 at 11:35 AM Johannes Weiner wrote: > > On Tue, Mar 28, 2023 at 06:16:35AM +0000, Yosry Ahmed wrote: > > > void mem_cgroup_flush_stats_ratelimited(void) > > > { > > > if (time_after64(jiffies_64, READ_ONCE(flush_next_time))) > > > - mem_cgroup_flush_stats(); > > > + mem_cgroup_flush_stats_atomic(); > > > +} > > > > This should probably be mem_cgroup_flush_stats_atomic_ratelimited(). > > > > (Whee, kinda long, but that's alright. Very specialized caller...) > > It should, but the following patch makes it non-atomic anyway, so I > thought I wouldn't clutter the diff by renaming it here and then > reverting it back in the next patch. > > There is an argument for maintaining a clean history tho in case the > next patch is reverted separately (which is the reason I put it in a > separate patch to begin with) -- so perhaps I should rename it here to > mem_cgroup_flush_stats_atomic_ratelimited () and back to > mem_cgroup_flush_stats_ratelimited() in the next patch, just for > consistency? Sounds good to me. It's pretty minor churn. > > Btw, can you guys think of a reason against moving the threshold check > > into the common function? It would then apply to the time-limited > > flushes as well, but that shouldn't hurt anything. This would make the > > code even simpler: > > I think the point of having the threshold check outside the common > function is that the periodic flusher always flushes, regardless of > the threshold, to keep rstat flushing from critical contexts as cheap > as possible. Good point. Yeah, let's keep it separate then. > > > @@ -2845,7 +2845,7 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc) > > > * Flush the memory cgroup stats, so that we read accurate per-memcg > > > * lruvec stats for heuristics. > > > */ > > > - mem_cgroup_flush_stats(); > > > + mem_cgroup_flush_stats_atomic(); > > > > I'm thinking this one could be non-atomic as well. It's called fairly > > high up in reclaim without any locks held. > > A later patch does exactly that. I put making the reclaim and refault > paths non-atomic in separate patches to easily revert them if we see a > regression. Let me know if this is too defensive and if you'd rather > have them squashed. No, good call. I should have just looked ahead first :-)