1 files changed, 17 insertions, 11 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cb1c9dedf9b6..194721839cf5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1199,7 +1199,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 
 			mz = mem_cgroup_zoneinfo(root, nid, zid);
 			iter = &mz->reclaim_iter[reclaim->priority];
-			last_visited = iter->last_visited;
 			if (prev && reclaim->generation != iter->generation) {
 				iter->last_visited = NULL;
 				goto out_unlock;
@@ -1218,13 +1217,12 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 			 * is alive.
 			 */
 			dead_count = atomic_read(&root->dead_count);
-			smp_rmb();
-			last_visited = iter->last_visited;
-			if (last_visited) {
-				if ((dead_count != iter->last_dead_count) ||
-					!css_tryget(&last_visited->css)) {
+			if (dead_count == iter->last_dead_count) {
+				smp_rmb();
+				last_visited = iter->last_visited;
+				if (last_visited &&
+				    !css_tryget(&last_visited->css))
 					last_visited = NULL;
-				}
 			}
 		}
 
@@ -3141,8 +3139,6 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
 			return -ENOMEM;
 		}
 
-		INIT_WORK(&s->memcg_params->destroy,
-				kmem_cache_destroy_work_func);
 		s->memcg_params->is_root_cache = true;
 
 		/*
@@ -4108,8 +4104,6 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
 	if (mem_cgroup_disabled())
 		return NULL;
 
-	VM_BUG_ON(PageSwapCache(page));
-
 	if (PageTransHuge(page)) {
 		nr_pages <<= compound_order(page);
 		VM_BUG_ON(!PageTransHuge(page));
@@ -4205,6 +4199,18 @@ void mem_cgroup_uncharge_page(struct page *page)
 	if (page_mapped(page))
 		return;
 	VM_BUG_ON(page->mapping && !PageAnon(page));
+	/*
+	 * If the page is in swap cache, uncharge should be deferred
+	 * to the swap path, which also properly accounts swap usage
+	 * and handles memcg lifetime.
+	 *
+	 * Note that this check is not stable and reclaim may add the
+	 * page to swap cache at any time after this.  However, if the
+	 * page is not in swap cache by the time page->mapcount hits
+	 * 0, there won't be any page table references to the swap
+	 * slot, and reclaim will free it and not actually write the
+	 * page to disk.
+	 */
 	if (PageSwapCache(page))
 		return;
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_ANON, false);