From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8C58331EC9 for ; Fri, 31 Jul 2026 02:42:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785465738; cv=none; b=u0zfCwly33AwVwjhLQc78MLvUiRVyEd2Nr09vTaePrkLyWvd8PpxbO0w333m0PfAu3BRuDNG85QrkM5sXdQhDDdn1kQUpMm7lmY33j35XcQiYFSdDQCNkQqrARSlm33t+jT6Oqs95V6R1RyzsMadRAI/sR1VH/K6WM5EFP45/x4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785465738; c=relaxed/simple; bh=xEPp3sRiUFFoHJm76c9naCdlwcm0oZxxiQHDoVx0N8Q=; h=Date:To:From:Subject:Message-Id; b=nbMYF8jOWSuZ2dFOCd8N/Q2uJqFOKWLQJWxSuBKrX0o2EoqZIf5xmqMFY8ddXzvfxd+6fTIeXVcYj6lz53rCHfx+cGoQXKwpZSY3xGvySSEf5/EQtHmpSyGPz5pWCGnR/76O0YY7cYRpgujFPDxQHuET801ddryimEQHxbGOyX4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=OZSMpJPy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="OZSMpJPy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E27A1F000E9; Fri, 31 Jul 2026 02:42:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785465736; bh=pot3ahI6b08Y0tlO3OYMgXhFCh+bW7HWev/MPbBGPE4=; h=Date:To:From:Subject; b=OZSMpJPy3o4RKvd4rFbnrbaVJ8kXhR3I7fZriZy36VGHVJLplAMPVdkiYNkJKYmQ4 h7WIdZ6xZukq0kmtOU0v6x3KVWvBRfONYRmbSBt0HzVQA+IT6opMkckeJgrO4THjY+ L4DdeKTaV8OU/II6cKWOz273Z35qhyFfKcFQo+vQ= Date: Thu, 30 Jul 2026 19:42:16 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,tj@kernel.org,surenb@google.com,shakeel.butt@linux.dev,rppt@kernel.org,roman.gushchin@linux.dev,mkoutny@suse.com,mhocko@suse.com,ljs@kernel.org,liam@infradead.org,hannes@cmpxchg.org,david@kernel.org,usama.arif@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-vmpressure-skip-tree=true-accounting-on-cgroup-v2.patch removed from -mm tree Message-Id: <20260731024216.8E27A1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/vmpressure: skip tree=true accounting on cgroup v2 has been removed from the -mm tree. Its filename was mm-vmpressure-skip-tree=true-accounting-on-cgroup-v2.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Usama Arif Subject: mm/vmpressure: skip tree=true accounting on cgroup v2 Date: Tue, 30 Jun 2026 04:23:32 -0700 Patch series "mm/vmpressure: reduce CPU, memory and code overhead on cgroup v2", v3. 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. This patch (of 2): vmpressure() has two outputs gated by the @tree argument: @tree=false drives in-kernel socket pressure (mem_cgroup_set_ socket_pressure), consumed by TCP/SCTP. This only applies on cgroup v2; on v1 socket memory is charged separately via tcpmem and the consumer reads memcg->tcpmem_pressure instead. @tree=true drives userspace eventfd notifications via the v1 memory.pressure_level / cgroup.event_control interface. v2 has no equivalent: userspace gets reclaim signals through memory.pressure (PSI), which does not touch vmpressure. The existing early return covered v1 + @tree=false. The symmetric v2 + @tree=true case was falling through and doing the full lock / accumulate / schedule_work / parent-walk dance for an events list that can never be populated. bpftrace on a 176-core production host (cgroup v2, CONFIG_MEMCG_V1=n, 285 memcgs, sustained reclaim) showed ~16,200 @tree=true vmpressure() calls per minute. Add an early return that skips cgroup v2 + tree = true which avoids us doing all this work. On a v2-only host this also eliminates a lock contention path that can serialise reclaimers on a single global sr_lock. [usama.arif@linux.dev: simplify the guard] Link: https://lore.kernel.org/e8e1a409-48d8-4fa7-ae98-49485a1607f6@linux.dev Link: https://lore.kernel.org/20260630112617.1198623-1-usama.arif@linux.dev Link: https://lore.kernel.org/20260630112617.1198623-2-usama.arif@linux.dev Signed-off-by: Usama Arif Acked-by: Shakeel Butt Acked-by: Johannes Weiner Cc: David Hildenbrand Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Michal Koutný Cc: Mike Rapoport Cc: Roman Gushchin Cc: Suren Baghdasaryan Cc: Tejun Heo Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/vmpressure.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/mm/vmpressure.c~mm-vmpressure-skip-tree=true-accounting-on-cgroup-v2 +++ a/mm/vmpressure.c @@ -246,11 +246,12 @@ void vmpressure(gfp_t gfp, int order, st return; /* - * The in-kernel users only care about the reclaim efficiency - * for this @memcg rather than the whole subtree, and there - * isn't and won't be any in-kernel user in a legacy cgroup. + * Only two combinations have a consumer: + * cgroup v2 + tree=false -> in-kernel socket pressure + * cgroup v1 + tree=true -> userspace eventfds (memory.pressure_level) + * Skip the other two: nothing consumes the result. */ - if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !tree) + if (cgroup_subsys_on_dfl(memory_cgrp_subsys) == tree) return; vmpr = memcg_to_vmpressure(memcg); _ Patches currently in -mm which might be from usama.arif@linux.dev are mm-mempolicy-skip-non-present-pmds-when-queueing-folios.patch mm-madvise-skip-device-private-pmds-in-cold-and-pageout-walks.patch mm-huge_memory-skip-device-private-pmds-in-madvise_free_huge_pmd.patch mm-vmstat-mm-memcontrol-add-_monotonic-vmstat-readers.patch mm-vmscan-reduce-lru_lock-contention-via-vmstat-derived-scan-balance-cost.patch