2 files changed, 19 insertions, 28 deletions

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 6a066a270fc5..dd88540bb995 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -376,14 +376,15 @@ cgroup might have some charge associated with it, even though all
 tasks have migrated away from it. (because we charge against pages, not
 against tasks.)
 
-Such charges are freed or moved to their parent. At moving, both of RSS
-and CACHES are moved to parent.
-rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also.
+We move the stats to root (if use_hierarchy==0) or parent (if
+use_hierarchy==1), and no change on the charge except uncharging
+from the child.
 
 Charges recorded in swap information is not updated at removal of cgroup.
 Recorded information is discarded and a cgroup which uses swap (swapcache)
 will be charged as a new owner of it.
 
+About use_hierarchy, see Section 6.
 
 5. Misc. interfaces.
 
@@ -396,13 +397,15 @@ will be charged as a new owner of it.
 
   Almost all pages tracked by this memory cgroup will be unmapped and freed.
   Some pages cannot be freed because they are locked or in-use. Such pages are
-  moved to parent and this cgroup will be empty. This may return -EBUSY if
-  VM is too busy to free/move all pages immediately.
+  moved to parent(if use_hierarchy==1) or root (if use_hierarchy==0) and this
+  cgroup will be empty.
 
   Typical use case of this interface is that calling this before rmdir().
   Because rmdir() moves all pages to parent, some out-of-use page caches can be
   moved to the parent. If you want to avoid that, force_empty will be useful.
 
+  About use_hierarchy, see Section 6.
+
 5.2 stat file
 
 memory.stat file includes following statistics
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1262a8bc402b..96cd9ebefb2c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2678,15 +2678,13 @@ static int mem_cgroup_move_parent(struct page *page,
                                   struct mem_cgroup *child,
                                   gfp_t gfp_mask)
 {
-        struct cgroup *cg = child->css.cgroup;
-        struct cgroup *pcg = cg->parent;
         struct mem_cgroup *parent;
         unsigned int nr_pages;
         unsigned long uninitialized_var(flags);
         int ret;
 
         /* Is ROOT ? */
-        if (!pcg)
+        if (mem_cgroup_is_root(child))
                 return -EINVAL;
 
         ret = -EBUSY;
@@ -2697,33 +2695,23 @@ static int mem_cgroup_move_parent(struct page *page,
 
         nr_pages = hpage_nr_pages(page);
 
-        parent = mem_cgroup_from_cont(pcg);
-        if (!parent->use_hierarchy) {
-                ret = __mem_cgroup_try_charge(NULL,
-                                        gfp_mask, nr_pages, &parent, false);
-                if (ret)
-                        goto put_back;
-        }
+        parent = parent_mem_cgroup(child);
+        /*
+         * If no parent, move charges to root cgroup.
+         */
+        if (!parent)
+                parent = root_mem_cgroup;
 
         if (nr_pages > 1)
                 flags = compound_lock_irqsave(page);
 
-        if (parent->use_hierarchy) {
-                ret = mem_cgroup_move_account(page, nr_pages,
-                                        pc, child, parent, false);
-                if (!ret)
-                        __mem_cgroup_cancel_local_charge(child, nr_pages);
-        } else {
-                ret = mem_cgroup_move_account(page, nr_pages,
-                                        pc, child, parent, true);
-
-                if (ret)
-                        __mem_cgroup_cancel_charge(parent, nr_pages);
-        }
+        ret = mem_cgroup_move_account(page, nr_pages,
+                                pc, child, parent, false);
+        if (!ret)
+                __mem_cgroup_cancel_local_charge(child, nr_pages);
 
         if (nr_pages > 1)
                 compound_unlock_irqrestore(page, flags);
-put_back:
         putback_lru_page(page);
 put:
         put_page(page);