(2012/03/29 2:37), Aneesh Kumar K.V wrote:

Michal Hocko [off-list ref] writes:

quoted

On Fri 16-03-12 23:09:24, Aneesh Kumar K.V wrote:
[...]

quoted

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6728a7a..4b36c5e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

[...]

quoted

@@ -4887,6 +5013,7 @@ err_cleanup:
 static struct cgroup_subsys_state * __ref
 mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 {
+	int idx;
 	struct mem_cgroup *memcg, *parent;
 	long error = -ENOMEM;
 	int node;

@@ -4929,9 +5056,14 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 		 * mem_cgroup(see mem_cgroup_put).
 		 */
 		mem_cgroup_get(parent);
+		for (idx = 0; idx < HUGE_MAX_HSTATE; idx++)
+			res_counter_init(&memcg->hugepage[idx],
+					 &parent->hugepage[idx]);

Hmm, I do not think we want to make groups deeper in the hierarchy
unlimited as we cannot reclaim. Shouldn't we copy the limit from the parent?
Still not ideal but slightly more expected behavior IMO.

But we should be limiting the child group based on parent's limit only
when hierarchy is set right ?

quoted

The hierarchy setups are still interesting and the limitations should be
described in the documentation...

It should behave similar to memcg. ie, if hierarchy is set, then we limit
using MIN(parent's limit, child's limit). May be I am missing some of
the details of memcg use_hierarchy config. My goal was to keep it
similar to memcg. Can you explain why do you think the patch would
make it any different ?

Maybe this is a different story but....

Tejun(Cgroup Maintainer) asked us to remove 'use_hierarchy' settings because
most of other cgroups are hierarchical(*). I answered that improvement in res_counter 
latency is required. And now, we have some idea to improve res_counter.
(I'd like to try this after page_cgroup diet series..)

If we change and drop use_hierarchy, the usage similar to current use_hierarchy=0
will be..

	/cgroup/memory/			       = unlimited
			level1		       = unlimited
				level2	       = unlimited
					level3 = limit

To do this, after improvement of res_counter, we entry use_hierarchy into
feature-removal-list and wait for 2 versions..So, this will not affect
your developments, anyway.
 
Thanks,
-Kame

(*) AFAIK, blkio cgroup needs tons of work to be hierarchical...