From ee9707e8593dfb9a375cf4793c3fd03d4142b463 Mon Sep 17 00:00:00 2001 From: Waiman Long <longman@redhat.com> Date: Wed, 11 Aug 2021 15:57:07 -0400 Subject: cgroup/cpuset: Enable memory migration for cpuset v2 When a user changes cpuset.cpus, each task in a v2 cpuset will be moved to one of the new cpus if it is not there already. For memory, however, they won't be migrated to the new nodes when cpuset.mems changes. This is an inconsistency in behavior. In cpuset v1, there is a memory_migrate control file to enable such behavior by setting the CS_MEMORY_MIGRATE flag. Make it the default for cpuset v2 so that we have a consistent set of behavior for both cpus and memory. There is certainly a cost to make memory migration the default, but it is a one time cost that shouldn't really matter as long as cpuset.mems isn't changed frequenty. Update the cgroup-v2.rst file to document the new behavior and recommend against changing cpuset.mems frequently. Since there won't be any concurrent access to the newly allocated cpuset structure in cpuset_css_alloc(), we can use the cheaper non-atomic __set_bit() instead of the more expensive atomic set_bit(). Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Tejun Heo <tj@kernel.org> --- kernel/cgroup/cpuset.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'kernel/cgroup') diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index fcc11f2d3b5b..44d234b0df5e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2761,12 +2761,16 @@ cpuset_css_alloc(struct cgroup_subsys_state *parent_css) return ERR_PTR(-ENOMEM); } - set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags); + __set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags); nodes_clear(cs->mems_allowed); nodes_clear(cs->effective_mems); fmeter_init(&cs->fmeter); cs->relax_domain_level = -1; + /* Set CS_MEMORY_MIGRATE for default hierarchy */ + if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) + __set_bit(CS_MEMORY_MIGRATE, &cs->flags); + return &cs->css; } -- cgit v1.2.3