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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1773190869; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=1zI0HjdpVIeLf9hsutuK6PY4JFf5qAhFtdlVI8aS1sw=; b=LgHUGplsk2p9syAn/wJWFocufn0GBEBbF/HLE+Hy6ni8L7uAVzEcVw7Zi4W98y97igwNd3 ct3hRgGLQHsuKtE95Av+ETz/CnvanrSyODESwHGyblTNbf6APrdMKTbSSTKZRvOn7KUPk/ Ju7/rXEFjmtKd1lL3Ymwc6MgnShnvxA= From: Shakeel Butt To: Tejun Heo Cc: Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Chen Ridong , Jakub Kicinski , Meta kernel team , linux-mm@kvack.org, netdev@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 0/3] cgroup: improve cgroup_file_notify() scalability Date: Tue, 10 Mar 2026 18:00:58 -0700 Message-ID: <20260311010101.3306366-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D6C55A0014 X-Stat-Signature: jdjp5phpa4udsch3it8ts3bg56q9yqmr X-Rspam-User: X-HE-Tag: 1773190871-985747 X-HE-Meta: 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 WI7LrJfF LhXTNg1xoihRtqjygmii40p2TOp3KU4/arpbUNleF6flJrOwVfzpfbcEo5Dla3+pblOevtwo3NZFpeDRpBGXq+nAD5FcUKFDVY/gQnpuNFLOi7GIR5bjLjyU0k+Hwq9g2DuXWihwAXKMdst8Lvqm9nmJ6tZ222QM60ePzsaRC4KbLvuVGp2IV696GIkMh4wpk7Mc05SIfi8toXUDz8JqLyVMCulkIoxIczNyZLke3f/AJ4vHhWSjfoeWynA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Jakub Kicinski reported that after the commit d929525c2e30 ("memcg: net: track network throttling due to memcg memory pressure"), in Meta fleet, the network intensive workloads started seeing extensive spinlock contention in the rx path in the function cgroup_file_notify(). cgroup_file_notify() uses a single global spinlock to protect the cfile->kn pointer across all cgroups. On systems with many cgroups under memory pressure, this becomes a bottleneck as multiple CPUs in reclaim call __memcg_memory_event(), which walks the cgroup hierarchy calling cgroup_file_notify() at each level -- all serialized on the same lock. This series reduces the lock hold time by moving kernfs_notify() outside the critical section, adds lockless fast-path checks to avoid the lock entirely in common cases (torn-down files and rate-limited bursts), and replaces the global lock with a per-cgroup_file lock to eliminate cross-cgroup contention. Changes since v1: - Second patch moves rate-limiting code out of lock Shakeel Butt (3): cgroup: reduce cgroup_file_kn_lock hold time in cgroup_file_notify() cgroup: add lockless fast-path checks to cgroup_file_notify() cgroup: replace global cgroup_file_kn_lock with per-cgroup_file lock include/linux/cgroup-defs.h | 1 + kernel/cgroup/cgroup.c | 53 ++++++++++++++++++++----------------- 2 files changed, 29 insertions(+), 25 deletions(-) -- 2.52.0