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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 4BE2516000D X-Rspam-User: X-Stat-Signature: ytiy7sknmqkt7tx66bpms3uzug95nmy3 X-HE-Tag: 1780746146-112290 X-HE-Meta: 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 sIpFl0Jx Fzr6W8VqEJsauVBVg+jW6jxmS8jiu/4W06GY2dHU4LFSVZOpbJDLMXgNOJ+p/X970BVfImSfNZOO5TDBcEKt5Ys6OkYpQg9oIvL6ynHox4jVEaXx+dOe/uw17I3Szn4R1ieOYrA68O5RTnoYSGivamzj0VtY3Wc1NZFEVx0q3krr81PYMutOTAPlZVtDT7IJkt/nFWyrh7acZ7pc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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