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From: Roman Gushchin To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Muchun Song , Vlastimil Babka , Axel Rasmussen , Steven Rostedt , Suren Baghdasaryan , Matthew Wilcox , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH v2] mm: mmap_lock: optimize mmap_lock tracepoints Message-ID: References: <20241125171617.113892-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241125171617.113892-1-shakeel.butt@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 4AE5F100009 X-Stat-Signature: ko4zuud8x3j3hybi3ief3xpfzuku35e9 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1732649359-152381 X-HE-Meta: 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 h0D6NZAW UW/PMx+t9igsgg0f+KEGVhSyAJ37b59x+PFgUFTpvHDK9Nn5DgYxOU+rw82OCV44u15z62262Nv0l7lUb+sBETrbIsw+d+7E8gMqGxF4gYSRcbn2GYd4Y1voT5Jg2RIuoPVpsIbpB5YY1FTNPmXxWYF5s6T9OSOsYeyX+76xAsRG0BVzSXoyx9Obl9yklnybGiXn3GYXSeYq3ZaOf6okLK+NXBw3NNtfST8v0FUh6K9BxA7w= 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 Mon, Nov 25, 2024 at 09:16:17AM -0800, Shakeel Butt wrote: > We are starting to deploy mmap_lock tracepoint monitoring across our > fleet and the early results showed that these tracepoints are consuming > significant amount of CPUs in kernfs_path_from_node when enabled. > > It seems like the kernel is trying to resolve the cgroup path in the > fast path of the locking code path when the tracepoints are enabled. In > addition for some application their metrics are regressing when > monitoring is enabled. > > The cgroup path resolution can be slow and should not be done in the > fast path. Most userspace tools, like bpftrace, provides functionality > to get the cgroup path from cgroup id, so let's just trace the cgroup > id and the users can use better tools to get the path in the slow path. > > Signed-off-by: Shakeel Butt Acked-by: Roman Gushchin Thanks!