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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780746131; 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=LXjmm9+ZvSlFJvfC2SPtLS5CK8YMB/c2K6dwL+Jj4J0=; b=UwI35iNnA4SH3IlinQwmGId/xrYwI4DKBtBSgf4Py4hWUGiO5ZRk0HFKOXfWKce1OzuaG0 HOCulQNOVifWQ/evGv8So4wJT/rCMBmTyyG1fxjSAiIA/vfNlSi7TufIsKkqn9Iu4WQx2P s52pEDBcwizSSZQaTC479XHAsP/xUCM= From: Usama Arif To: Andrew Morton , david@kernel.org, linux-mm@kvack.org Cc: hannes@cmpxchg.org, tj@kernel.org, mkoutny@suse.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, kernel-team@meta.com, Usama Arif Subject: [PATCH 0/2] mm/vmpressure: reduce CPU, memory and code overhead on cgroup v2 Date: Sat, 6 Jun 2026 04:41:32 -0700 Message-ID: <20260606114158.3126210-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 038614000B X-Stat-Signature: ec18owkhocynmfsjhkgbjuxzpgoxpotj X-HE-Tag: 1780746133-944552 X-HE-Meta: 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 hxePhLin 9ax0/wrHZe6BnI8w7AGbP08VoX4KwxEe+Uu/l4bEhLJbn/2GEuJvrkdE33L73IaJkkwO3UGNKGsvWINYBhy55UtoCw5mqIDwK+Y94Bxc1tGzc3T7XmUorAY+aEixN9qKwNHN1q7gou8nvOPWmE2DBk+XuoWxNXcjNaUhVPggOLhBifiOQ/f6zDKSe4rT8Mj/FmA1H Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The vmpressure subsystem has two distinct consumers, gated by the @tree argument: tree=false : in-kernel socket pressure, consumed by TCP/SCTP. This is cgroup v2 only; v1 sockets read memcg->tcpmem_pressure instead. tree=true : cgroup v1 userspace eventfd notifications via the memory.pressure_level / cgroup.event_control interface. v2 has no equivalent (userspace gets reclaim signals through memory.pressure / PSI, which doesn't touch vmpressure). So of the four (hierarchy, tree) combinations, only two carry data that anyone reads. The existing early return in vmpressure() covered v1 + tree=false; the symmetric v2 + tree=true case was falling through and doing the full lock / accumulate / schedule_work / parent-walk dance, even though the events list it eventually iterates is empty on cgroup v2 (vmpressure_register_event() is wired up only through the v1 cftype "memory.pressure_level" and can't be reached from a v2 memcg). Patch 1 extends the existing early return to also skip v2 + tree=true. On a v2-only host this eliminates a contended path where reclaimers can serialize on a single global sr_lock. bpftrace on a 176-core production host (cgroup v2, 285 memcgs, sustained reclaim) showed ~16,200 such calls per minute with tree = true. Patch 2 follows up with a cleanup: it splits the v1 userspace eventfd interface (struct vmpressure_event, the events list and its mutex, the work_struct and its handler, the parent walk, vmpressure_register_event / unregister_event, and vmpressure_prio) into a new mm/vmpressure-v1.c built only when CONFIG_MEMCG_V1=y, behind small no-op stubs in the header. mm/vmpressure.c keeps the shared bits and the tree=false socket-pressure path. The size of vmpressure.c goes down to half and the code is much more simpler. The only #ifdef CONFIG_MEMCG_V1 remaining in source is around the v1-only fields inside struct vmpressure itself. Memory savings on CONFIG_MEMCG_V1=n: struct vmpressure : 112B -> 24B struct mem_cgroup : 1664B -> 1536B Usama Arif (2): mm/vmpressure: skip tree=true accounting on cgroup v2 mm/vmpressure: split v1 userspace eventfd code into vmpressure-v1.c include/linux/vmpressure.h | 46 +++++- mm/Makefile | 2 +- mm/vmpressure-v1.c | 305 +++++++++++++++++++++++++++++++++++++ mm/vmpressure.c | 303 +++--------------------------------- 4 files changed, 364 insertions(+), 292 deletions(-) create mode 100644 mm/vmpressure-v1.c -- 2.52.0