[mm] [PATCH 4/4] Memory cgroup hierarchy feature selector

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Don't enable multiple hierarchy support by default. This patch introduces
a features element that can be set to enable the nested depth hierarchy
feature. This feature can only be enabled when there is just one cgroup
(the root cgroup).

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---

 mm/memcontrol.c |   38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff -puN mm/memcontrol.c~memcg-add-hierarchy-selector mm/memcontrol.c
--- linux-2.6.28-rc2/mm/memcontrol.c~memcg-add-hierarchy-selector	2008-11-02 00:15:00.000000000 +0530
+++ linux-2.6.28-rc2-balbir/mm/memcontrol.c	2008-11-02 00:15:00.000000000 +0530
@@ -40,6 +40,9 @@
 struct cgroup_subsys mem_cgroup_subsys __read_mostly;
 #define MEM_CGROUP_RECLAIM_RETRIES	5
 
+static unsigned long mem_cgroup_features;
+#define MEM_CGROUP_FEAT_HIERARCHY	0x1
+
 /*
  * Statistics for memory cgroup.
  */
@@ -1080,6 +1083,31 @@ out:
 	return ret;
 }
 
+static u64 mem_cgroup_feature_read(struct cgroup *cont, struct cftype *cft)
+{
+	return mem_cgroup_features;
+}
+
+static int mem_cgroup_feature_write(struct cgroup *cont, struct cftype *cft,
+			    		u64 val)
+{
+	int retval = 0;
+	struct cgroup *cgroup = init_mem_cgroup.css.cgroup;
+
+	if (val & MEM_CGROUP_FEAT_HIERARCHY) {
+		if (list_empty(&cgroup->children))
+			mem_cgroup_features |= MEM_CGROUP_FEAT_HIERARCHY;
+		else
+			retval = -EBUSY;
+	} else {
+		if (list_empty(&cgroup->children))
+			mem_cgroup_features &= ~MEM_CGROUP_FEAT_HIERARCHY;
+		else
+			retval = -EBUSY;
+	}
+	return retval;
+}
+
 static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
 {
 	return res_counter_read_u64(&mem_cgroup_from_cont(cont)->res,
@@ -1214,6 +1242,11 @@ static struct cftype mem_cgroup_files[] 
 		.name = "stat",
 		.read_map = mem_control_stat_show,
 	},
+	{
+		.name = "features",
+		.write_u64 = mem_cgroup_feature_write,
+		.read_u64 = mem_cgroup_feature_read,
+	},
 };
 
 static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
@@ -1292,7 +1325,10 @@ mem_cgroup_create(struct cgroup_subsys *
 			return ERR_PTR(-ENOMEM);
 	}
 
-	res_counter_init(&mem->res, parent ? &parent->res : NULL);
+	if ((mem_cgroup_features & MEM_CGROUP_FEAT_HIERARCHY) && parent)
+		res_counter_init(&mem->res, &parent->res);
+	else
+		res_counter_init(&mem->res, NULL);
 
 	for_each_node_state(node, N_POSSIBLE)
 		if (alloc_mem_cgroup_per_zone_info(mem, node))
_

-- 
	Balbir