[RFC][PATCH] memcg: show real limit under hierarchy

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

I wonder other people who debugs memcg's hierarchy may use similar patches.
this is my one.
comments ?
==
From:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Show "real" limit of memcg.
This helps my debugging and maybe useful for users.

While testing hierarchy like this

	mount -t cgroup none /cgroup -t memory
	mkdir /cgroup/A
	set use_hierarchy==1 to "A"
	mkdir /cgroup/A/01
	mkdir /cgroup/A/01/02
	mkdir /cgroup/A/01/03
	mkdir /cgroup/A/01/03/04
	mkdir /cgroup/A/08
	mkdir /cgroup/A/08/01
	....
and set each own limit to them, "real" limit of each memcg is unclear.
This patch shows real limit by checking all ancestors in memory.stat.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/memcontrol.c |   37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

Index: mmotm-2.6.28-Dec09/mm/memcontrol.c
===================================================================
--- mmotm-2.6.28-Dec09.orig/mm/memcontrol.c
+++ mmotm-2.6.28-Dec09/mm/memcontrol.c
@@ -1758,6 +1758,36 @@ static int mem_cgroup_write(struct cgrou
 	return ret;
 }
 
+static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
+		unsigned long long *mem_limit, unsigned long long *memsw_limit)
+{
+	struct cgroup *cgroup;
+	unsigned long long min_limit, min_memsw_limit, tmp;
+
+	min_limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
+	min_memsw_limit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
+	cgroup = memcg->css.cgroup;
+	if (!memcg->use_hierarchy)
+		goto out;
+
+	while (cgroup->parent) {
+		cgroup = cgroup->parent;
+		memcg = mem_cgroup_from_cont(cgroup);
+		if (!memcg->use_hierarchy)
+			break;
+		tmp = res_counter_read_u64(&memcg->res, RES_LIMIT);
+		if (tmp < min_limit)
+			min_limit = tmp;
+		tmp = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
+		if (tmp < min_memsw_limit)
+			min_memsw_limit = tmp;
+	}
+out:
+	*mem_limit = min_limit;
+	*memsw_limit = min_memsw_limit;
+	return;
+}
+
 static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
 {
 	struct mem_cgroup *mem;
@@ -1831,6 +1861,13 @@ static int mem_control_stat_show(struct 
 		cb->fill(cb, "unevictable", unevictable * PAGE_SIZE);
 
 	}
+	{
+		unsigned long long limit, memsw_limit;
+		memcg_get_hierarchical_limit(mem_cont, &limit, &memsw_limit);
+		cb->fill(cb, "hierarchical_memory_limit", limit);
+		if (do_swap_account)
+			cb->fill(cb, "hierarchical_memsw_limit", memsw_limit);
+	}
 
 #ifdef CONFIG_DEBUG_VM
 	cb->fill(cb, "inactive_ratio", mem_cont->inactive_ratio);