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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782818790; 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=FedLfmQ5jQup09b0jvVq17NcnfWVfzz13Rawjxlqaw0=; b=DgM03IMwPfYvkxpS+yWuDb8XUVmz0XITjkiTan3sS5+RXSFBQGCSG8HzCPkAeeRvtYeUxk TdiSmH09BxhKECRq85Ph/eTGMpHCKepbHj6C76Rah+Ous+orL7H43PDtMthsj+qRrHHnTP Onp97M+PlxF36vSxEqMhlRqi/+GKUMA= 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 v3 0/2] mm/vmpressure: reduce CPU, memory and code overhead on cgroup v2 Date: Tue, 30 Jun 2026 04:23:31 -0700 Message-ID: <20260630112617.1198623-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: gepzisq6gc6babqwxccmbuu1ky3g7c8s X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4D5DCC0002 X-HE-Tag: 1782818792-786993 X-HE-Meta: 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 BALDZnKC MwrPl4X4b4M7j6WK7+Fc6TqOJEJ+JciY7MX54p5TpXrmZyy0Tlbu5qph8xp0UWUaNIpH5EDP00foff1WYw53u/duMpEsLnlgKDuobV9Iik2SlXuAt7MNVTTOhTUttgPl4z4p5XLYd+n+EmnqyuoE0U11W6z4MRYdDSyBKfGmtvRjJAGFD3L2+rZMMqq7brjtodlSvRU1SA2q1KgDNZK8XU6zhFmCWvUOAQJvc 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/memcontrol-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 This split is the first step toward eventually making vmpressure CONFIG_MEMCG_V1 only. The v2 in-kernel socket pressure path (tree=false) cannot be removed today immediately: PSI is not an exact replacement for vmpressure, and switching networking socket-buffer back-off to PSI may regress networking performance or increase memory pressure in workloads that today rely on vmpressure's hysteresis. The medium-term plan is to introduce a PSI-based socket-pressure path, keep vmpressure available for v2 behind a defconfig as an opt-out for several releases, and only then drop the tree=false path entirely, at which point everything that remains in mm/memcontrol-v1.c is the whole subsystem. --- v2 -> v3: https://lore.kernel.org/all/20260629130042.2649505-1-usama.arif@linux.dev/ - Move the cgroup v1 code into memcontrol-v1.c instead of creating a new file (Johannes) v1 -> v2: https://lore.kernel.org/all/20260606114158.3126210-1-usama.arif@linux.dev/ - Add more in commit message about future plans of vmpressure for cgroup v2 (Shakeel) - Remove unnecessary return statement in vmpressure for v1 only tree path (Michal) - Rebased onto latest mm-new Usama Arif (2): mm/vmpressure: skip tree=true accounting on cgroup v2 mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c include/linux/vmpressure.h | 46 +++++- mm/memcontrol-v1.c | 292 +++++++++++++++++++++++++++++++++++ mm/vmpressure.c | 302 ++----------------------------------- 3 files changed, 349 insertions(+), 291 deletions(-) -- 2.53.0-Meta