From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 2852F3947AE for ; Sat, 6 Jun 2026 11:42:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780746148; cv=none; b=UTmh3QDowKmOrbFfhT5vuv78C/biyhSHhIL2AZVFI+X3TpdW6n8JWQW9+jjfn8gUcAnm8k4Alhx9bLvuNsZjnBcJ2T/912MP8outtfDY1fAvKJVGN9oDD3l++C43ABWjB1JxA8TV7nG/lGMh4SZyJs6oAiLWrlXBT3luWmdJEOE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780746148; c=relaxed/simple; bh=9Z7zGEc5G0wKjEoqdIK3pL5sKV3WOw+oaGvjsJHNKnc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HggXDCzx9fXJkekQ+KaLpeZeqLbe+2ol9lmLOoSxKPAmU44V5tqFlyvHSPkpGnX6moMurDEns7T+ILezIz1nsCTbhDm1U+G3hBd5lej4jNw0DLnzagO4K7rqQogzm/auULNPnzKt/ZEBWEtxVZ4FbROWa1VBPX17Uv77ev/yhxs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Sh2DPYgB; arc=none smtp.client-ip=91.218.175.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Sh2DPYgB" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780746144; 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: in-reply-to:in-reply-to:references:references; bh=AjLkqSwz++whBKGw/N3/SE9JcCfj2BM6NfCAXyiYS+A=; b=Sh2DPYgBxZ8VwZuzhQMnbgiEqWZiE+nUlYUyBuWGjT+kloUbH0iUkengc6osoNJIdkfylQ 2VvpHi5wiK2b60MRk2aBuMRBOwZJgqM692yi3nVONHldLJO6VvfWvE82E63qjiaAN24lUV AAcmoIDoe9+TAAZOLPnB+u1c9Vr2Rss= 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 1/2] mm/vmpressure: skip tree=true accounting on cgroup v2 Date: Sat, 6 Jun 2026 04:41:33 -0700 Message-ID: <20260606114158.3126210-2-usama.arif@linux.dev> In-Reply-To: <20260606114158.3126210-1-usama.arif@linux.dev> References: <20260606114158.3126210-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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. Signed-off-by: Usama Arif --- mm/vmpressure.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/mm/vmpressure.c b/mm/vmpressure.c index f053554e5826..c82cee1ab43b 100644 --- a/mm/vmpressure.c +++ b/mm/vmpressure.c @@ -246,11 +246,13 @@ void vmpressure(gfp_t gfp, int order, struct mem_cgroup *memcg, bool tree, 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) || + (cgroup_subsys_on_dfl(memory_cgrp_subsys) && tree)) return; vmpr = memcg_to_vmpressure(memcg); -- 2.52.0