From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) (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 83320404BCA for ; Mon, 29 Jun 2026 13:00:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782738057; cv=none; b=gMM5hZnSHtUNjPP98OK+q3GxCLbh5EOqLhn21/PnQguvwYglT7PMdbgDOJbGR0l++GUNbYn3+G7sUfvON1JowczcnBNZChxqJUYLtW3mnRT0nPUw3R2eAM9uyh44+G9VbeAwMQsWMUFvy8a1CogsphRrHvpI7dX2HE+xnoz36dQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782738057; c=relaxed/simple; bh=QKVHBhDJOmBmKNy1mcKVauBAX5xGjaRKrFEXGUuurqE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dtXpEdibH/nMgip0efF72s7ifLTTx4sZOqrO3M6ONz1ogQ1vzWupkvLOdkkbAFL3KEzl9JwV0KicRdu3zXr8t53WHl58e88v/WrcWcsizwUriZFDYWjewihvSOWylkFv9pNXE5BYftajtEPZBcANSbUmL17ThAEC1DiznVSgZws= 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=Tq07vjhl; arc=none smtp.client-ip=95.215.58.176 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="Tq07vjhl" 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=1782738053; 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=3Mj2gt/hTNZzbuZtdAFTmoZ+udDIFe1awW9U5cT+0b8=; b=Tq07vjhl1bPKN9Z63p9ufM43vhudCB5raWPV/KUTdZ9voQE2TI3vu89IcpO2wmPowcgJVG xtEBN80W1RgfrbgXx52uEU1ufqhctorpGvEZFp2o1J/R0BtEpyMaGmtAFT9Z88h2r2D5Ks +WhAn8Ftb9wc6n5nvBSwokO27VAuVw4= 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 v2 1/2] mm/vmpressure: skip tree=true accounting on cgroup v2 Date: Mon, 29 Jun 2026 05:59:36 -0700 Message-ID: <20260629130042.2649505-2-usama.arif@linux.dev> In-Reply-To: <20260629130042.2649505-1-usama.arif@linux.dev> References: <20260629130042.2649505-1-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. Acked-by: Shakeel Butt 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); -- 2.53.0-Meta