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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BE1E640006 X-Stat-Signature: o9o96b1r7psd1heaa443qk58ns1cx9h8 X-HE-Tag: 1782738054-762341 X-HE-Meta: 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 bPjytduD H5M55dG/2ijceSpAw5nE+6rsOnhQTh13HxACWBkoGIu4Snq2hrAxwQu1A5d/gQcZzrQB22OlcEJczsltppklrJzqUdXrVVStsZuNkQLRf805zDPnQBQwleNdvfJImzvdWPcywchhNGJmj/3ZELojDL6XfdsKoYQ96D9Dw6/KrAPdNHM/98vGlI2RhdvDSJGTXF6LiDyRYDqelVWk= 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. 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