1 files changed, 48 insertions, 28 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 916132a29b36..5a1d584ffed3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2702,10 +2702,27 @@ out:
         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));
 }
 
 /*
@@ -3747,7 +3767,6 @@ 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))
@@ -3755,28 +3774,30 @@ static int mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
                 /* 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