---

yaml
---
r: 339309
b: refs/heads/master
c: 2ef37d3
h: refs/heads/master
i:
  339307: 4d78a36
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d842301181d9a4486aa24720ed4f96018b213292
+refs/heads/master: 2ef37d3fe474b218e170010a59066e19427c9847

trunk/mm/memcontrol.c

@@ -2702,10 +2702,27 @@ static int mem_cgroup_move_account(struct page *page,
 	return ret;
 }
 
-/*
- * move charges to its parent.
+/**
+ * mem_cgroup_move_parent - moves page to the parent group
+ * @page: the page to move
+ * @pc: page_cgroup of the page
+ * @child: page's cgroup
+ *
+ * move charges to its parent or the root cgroup if the group has no
+ * parent (aka use_hierarchy==0).
+ * Although this might fail (get_page_unless_zero, isolate_lru_page or
+ * mem_cgroup_move_account fails) the failure is always temporary and
+ * it signals a race with a page removal/uncharge or migration. In the
+ * first case the page is on the way out and it will vanish from the LRU
+ * on the next attempt and the call should be retried later.
+ * Isolation from the LRU fails only if page has been isolated from
+ * the LRU since we looked at it and that usually means either global
+ * reclaim or migration going on. The page will either get back to the
+ * LRU or vanish.
+ * Finaly mem_cgroup_move_account fails only if the page got uncharged
+ * (!PageCgroupUsed) or moved to a different group. The page will
+ * disappear in the next attempt.
  */
-
 static int mem_cgroup_move_parent(struct page *page,
 				  struct page_cgroup *pc,
 				  struct mem_cgroup *child)
@@ -2732,8 +2749,10 @@ static int mem_cgroup_move_parent(struct page *page,
 	if (!parent)
 		parent = root_mem_cgroup;
 
-	if (nr_pages > 1)
+	if (nr_pages > 1) {
+		VM_BUG_ON(!PageTransHuge(page));
 		flags = compound_lock_irqsave(page);
+	}
 
 	ret = mem_cgroup_move_account(page, nr_pages,
 				pc, child, parent);
@@ -3683,17 +3702,22 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 	return nr_reclaimed;
 }
 
-/*
+/**
+ * mem_cgroup_force_empty_list - clears LRU of a group
+ * @memcg: group to clear
+ * @node: NUMA node
+ * @zid: zone id
+ * @lru: lru to to clear
+ *
  * Traverse a specified page_cgroup list and try to drop them all.  This doesn't
- * reclaim the pages page themselves - it just removes the page_cgroups.
- * Returns true if some page_cgroups were not freed, indicating that the caller
- * must retry this operation.
+ * reclaim the pages page themselves - pages are moved to the parent (or root)
+ * group.
  */
-static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
+static void mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 				int node, int zid, enum lru_list lru)
 {
 	struct mem_cgroup_per_zone *mz;
-	unsigned long flags, loop;
+	unsigned long flags;
 	struct list_head *list;
 	struct page *busy;
 	struct zone *zone;
@@ -3702,11 +3726,8 @@ static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 	mz = mem_cgroup_zoneinfo(memcg, node, zid);
 	list = &mz->lruvec.lists[lru];
 
-	loop = mz->lru_size[lru];
-	/* give some margin against EBUSY etc...*/
-	loop += 256;
 	busy = NULL;
-	while (loop--) {
+	do {
 		struct page_cgroup *pc;
 		struct page *page;
 
@@ -3732,8 +3753,7 @@ static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 			cond_resched();
 		} else
 			busy = NULL;
-	}
-	return !list_empty(list);
+	} while (!list_empty(list));
 }
 
 /*
@@ -3747,36 +3767,37 @@ static int mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
 {
 	struct cgroup *cgrp = memcg->css.cgroup;
 	int node, zid;
-	int ret;
 
 	do {
 		if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
 			return -EBUSY;
 		/* This is for making all *used* pages to be on LRU. */
 		lru_add_drain_all();
 		drain_all_stock_sync(memcg);
-		ret = 0;
 		mem_cgroup_start_move(memcg);
 		for_each_node_state(node, N_HIGH_MEMORY) {
-			for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
+			for (zid = 0; zid < MAX_NR_ZONES; zid++) {
 				enum lru_list lru;
 				for_each_lru(lru) {
-					ret = mem_cgroup_force_empty_list(memcg,
+					mem_cgroup_force_empty_list(memcg,
 							node, zid, lru);
-					if (ret)
-						break;
 				}
 			}
-			if (ret)
-				break;
 		}
 		mem_cgroup_end_move(memcg);
 		memcg_oom_recover(memcg);
 		cond_resched();
-	/* "ret" should also be checked to ensure all lists are empty. */
-	} while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
 
-	return ret;
+		/*
+		 * This is a safety check because mem_cgroup_force_empty_list
+		 * could have raced with mem_cgroup_replace_page_cache callers
+		 * so the lru seemed empty but the page could have been added
+		 * right after the check. RES_USAGE should be safe as we always
+		 * charge before adding to the LRU.
+		 */
+	} while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0);
+
+	return 0;
 }
 
 /*
@@ -5618,7 +5639,6 @@ struct cgroup_subsys mem_cgroup_subsys = {
 	.base_cftypes = mem_cgroup_files,
 	.early_init = 0,
 	.use_id = 1,
-	.__DEPRECATED_clear_css_refs = true,
 };
 
 #ifdef CONFIG_MEMCG_SWAP