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From: Shakeel Butt To: Waiman Long Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Yosry Ahmed , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH] memcg: optimize memcg_rstat_updated Message-ID: References: <20250409234908.940121-1-shakeel.butt@linux.dev> <2f9d478d-3359-40c8-8607-be906eaeea04@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f9d478d-3359-40c8-8607-be906eaeea04@redhat.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 31722140013 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: w9o6y5o5oh4i55nn5fc6z9nbabjom1zn X-HE-Tag: 1744249795-255455 X-HE-Meta: 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 BoMnLzgg gtcB8nyx9pwcnOcJSgdhHwQ6LJ9b2D0vCQiCSia6FgbGMHKQuAnDzvyIeX5L5k4E9EZCcIr1wQo3DzAt89CdA2zLRFe/WrAD2JxjK9LS7YXyTwL9QuY4UE6/3Ef+NuLLifYF+xFv9NkV7dnnX+i2soJqCK8fdh2fseTJ/XAI4fwyE29SP04c4SDAUfPd9Serl0Ir1NKdQI1j7sbRKHo1l79E6Md6WnoZe/sAH 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: List-Subscribe: List-Unsubscribe: On Wed, Apr 09, 2025 at 09:20:34PM -0400, Waiman Long wrote: > On 4/9/25 7:49 PM, Shakeel Butt wrote: > > Currently the kernel maintains the stats updates per-memcg which is > > needed to implement stats flushing threshold. On the update side, the > > update is added to the per-cpu per-memcg update of the given memcg and > > all of its ancestors. However when the given memcg has passed the > > flushing threshold, all of its ancestors should have passed the > > threshold as well. There is no need to traverse up the memcg tree to > > maintain the stats updates. > > > > Perf profile collected from our fleet shows that memcg_rstat_updated is > > one of the most expensive memcg function i.e. a lot of cumulative CPU > > is being spent on it. So, even small micro optimizations matter a lot. > > > > Signed-off-by: Shakeel Butt > > --- > > mm/memcontrol.c | 16 +++++++++------- > > 1 file changed, 9 insertions(+), 7 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 421740f1bcdc..ea3e40e589df 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -585,18 +585,20 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val) > > cgroup_rstat_updated(memcg->css.cgroup, cpu); > > statc = this_cpu_ptr(memcg->vmstats_percpu); > > for (; statc; statc = statc->parent) { > > + /* > > + * If @memcg is already flushable then all its ancestors are > > + * flushable as well and also there is no need to increase > > + * stats_updates. > > + */ > > + if (!memcg_vmstats_needs_flush(statc->vmstats)) > > + break; > > + > > Do you mean "if (memcg_vmstats_needs_flush(statc->vmstats))"? > Yup you are right, thanks for catching this. I will send a v2.