Hello,

On Fri, Aug 28, 2015 at 07:49:18PM +0300, Vladimir Davydov wrote:

On Fri, Aug 28, 2015 at 11:25:30AM -0400, Tejun Heo wrote:

quoted

On the default hierarchy, all memory consumption will be accounted
together and controlled by the same set of limits.  Always enable
kmemcg on the default hierarchy.

IMO we should introduce a boot time knob for disabling it, because kmem
accounting is still not perfect, besides some users might prefer to go
w/o it for performance reasons.

Yeah, fair enough.

quoted

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c94b686..8a5dd01 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -4362,6 +4362,13 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	if (ret)
 		return ret;
 
+	/* kmem is always accounted together on the default hierarchy */
+	if (cgroup_on_dfl(css->cgroup)) {
+		ret = memcg_activate_kmem(memcg, PAGE_COUNTER_MAX);
+		if (ret)
+			return ret;
+	}
+

This is a wrong place for this. The kernel will panic on an attempt to
create a sub memcg, because memcg_init_kmem already enables kmem
accounting in this case. I guess we should add this hunk to
memcg_propagate_kmem instead.

Yeap, bypassing "parent is active" test in memcg_propagate_kmem()
seems like the right thing to do.

Thanks.

-- 
tejun

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