[PATCH 4/6] memcg: simplify mem_cgroup_page_stat()

[Greg Thelen <gthelen@google.com>]

The cgroup given to mem_cgroup_page_stat() is no allowed to be
NULL or the root cgroup.  So there is no need to complicate the code
handling those cases.

Signed-off-by: Greg Thelen <gthelen@google.com>
---
 mm/memcontrol.c |   48 ++++++++++++++++++++++--------------------------
 1 files changed, 22 insertions(+), 26 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eb621ee..f8df350 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1364,12 +1364,10 @@ memcg_hierarchical_free_pages(struct mem_cgroup *mem)
 
 /*
  * mem_cgroup_page_stat() - get memory cgroup file cache statistics
- * @mem:	optional memory cgroup to query.  If NULL, use current task's
- *		cgroup.
+ * @mem:	memory cgroup to query
  * @item:	memory statistic item exported to the kernel
  *
- * Return the accounted statistic value or negative value if current task is
- * root cgroup.
+ * Return the accounted statistic value.
  */
 long mem_cgroup_page_stat(struct mem_cgroup *mem,
 			  enum mem_cgroup_nr_pages_item item)
@@ -1377,29 +1375,27 @@ long mem_cgroup_page_stat(struct mem_cgroup *mem,
 	struct mem_cgroup *iter;
 	long value;
 
+	VM_BUG_ON(!mem);
+	VM_BUG_ON(mem_cgroup_is_root(mem));
+
 	get_online_cpus();
-	rcu_read_lock();
-	if (!mem)
-		mem = mem_cgroup_from_task(current);
-	if (__mem_cgroup_has_dirty_limit(mem)) {
-		/*
-		 * If we're looking for dirtyable pages we need to evaluate
-		 * free pages depending on the limit and usage of the parents
-		 * first of all.
-		 */
-		if (item == MEMCG_NR_DIRTYABLE_PAGES)
-			value = memcg_hierarchical_free_pages(mem);
-		else
-			value = 0;
-		/*
-		 * Recursively evaluate page statistics against all cgroup
-		 * under hierarchy tree
-		 */
-		for_each_mem_cgroup_tree(iter, mem)
-			value += mem_cgroup_local_page_stat(iter, item);
-	} else
-		value = -EINVAL;
-	rcu_read_unlock();
+
+	/*
+	 * If we're looking for dirtyable pages we need to evaluate
+	 * free pages depending on the limit and usage of the parents
+	 * first of all.
+	 */
+	if (item == MEMCG_NR_DIRTYABLE_PAGES)
+		value = memcg_hierarchical_free_pages(mem);
+	else
+		value = 0;
+	/*
+	 * Recursively evaluate page statistics against all cgroup
+	 * under hierarchy tree
+	 */
+	for_each_mem_cgroup_tree(iter, mem)
+		value += mem_cgroup_local_page_stat(iter, item);
+
 	put_online_cpus();
 
 	return value;
-- 
1.7.3.1

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