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