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AJvYcCUr4vCoKfN1NWXtdn5jSDvRsqEdOS8gTCPgcWHNyfzkwDJNCEGHzdaYRz6tSZgxka7vBOgDOceN9Q==@kvack.org X-Gm-Message-State: AOJu0Yzgq4nzv0iIhNBwX1XzqolRs8sTSH64eLivWG/s/2Zo5r971zIK ujd8lTJUL0qm3SjjTWkFBGAT9wqJRw/IOqiiDTwYTy/G4JvdlJtdfvRpeVtTdr2NzPSsxhjZ3tH /R68wpA6WNsjZd7S6rDj+phgdQ0+7sc0x12qI X-Gm-Gg: ASbGncuxNWMjVEUMV2Pe/5rOTkOH8WIHBEl+ZlzH4Ku0F0at872zsGjtlhCANor3nwg NJ1C3MPP+KCjWlsG1mriM3enhTBZBydFk/1gssN5In2svyuOFtOuSo7uSDxc= X-Google-Smtp-Source: AGHT+IG+kehlB4s0M5dWyJKGLHeYyY36EY44ty+lp0Mvoe5e9HkKe9gEegCulaT0+L4A1Oxd2n33hHXL6WkpLXJ43p4= X-Received: by 2002:a05:600c:3b28:b0:42b:8ff7:bee2 with SMTP id 5b1f17b1804b1-434b066ec64mr85985e9.5.1732738218634; Wed, 27 Nov 2024 12:10:18 -0800 (PST) MIME-Version: 1.0 References: <20241125171617.113892-1-shakeel.butt@linux.dev> In-Reply-To: From: Axel Rasmussen Date: Wed, 27 Nov 2024 12:09:42 -0800 Message-ID: Subject: Re: [PATCH v2] mm: mmap_lock: optimize mmap_lock tracepoints To: Roman Gushchin Cc: Shakeel Butt , Andrew Morton , Johannes Weiner , Michal Hocko , Muchun Song , Vlastimil Babka , Steven Rostedt , Suren Baghdasaryan , Matthew Wilcox , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AE5D61C0012 X-Stat-Signature: npyf75b7fj7j7bdrpe99ak4k8hc58t9j X-Rspam-User: X-HE-Tag: 1732738217-782277 X-HE-Meta: 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 JpWy9VqU nClx7tgRXJhh8p36SqnMEnoOSexPrJ6ROxOhYqazOpuZ9pslFcbhv9jv1Ubn+EeKOAZZdWUoQBPccBIMDRMCBxCeb2bXnx03Wc/fq6ecRZzfvf1YQDzIuYkQ8BDdeu7hpUMuI0dWqTvBviXDbU8ZeazvjVTszCNv+8DebHor/If8dTjMMrJZk5MZ23oGLsVmiBKYrrDijDpsvA9ownm8vwFdVghH5FWZrU2OKdRR+caeTTMbaRqzh1+c/UzMSvg0wA9ReGjzdLs112SUz2bNoBzIDCrzhVznCVfsgZw6P1SXdIZg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: No objections. :) Reviewed-by: Axel Rasmussen On Tue, Nov 26, 2024 at 11:29=E2=80=AFAM Roman Gushchin wrote: > > 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!