memcg: avoid unnecessary initialization

* remove over-killing initialization (in fast path)
* makeing the condition for PAGE_CGROUP_FLAG_ACTIVE be more obvious.

Signed-off-by: KAMEAZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -296,7 +296,7 @@ static void __mem_cgroup_remove_list(struct mem_cgroup_per_zone *mz,
 		MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE) -= 1;
 
 	mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, false);
-	list_del_init(&pc->lru);
+	list_del(&pc->lru);
 }
 
 static void __mem_cgroup_add_list(struct mem_cgroup_per_zone *mz,
@@ -559,7 +559,7 @@ retry:
 	}
 	unlock_page_cgroup(page);
 
-	pc = kmem_cache_zalloc(page_cgroup_cache, gfp_mask);
+	pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
 	if (pc == NULL)
 		goto err;
 
@@ -606,9 +606,14 @@ retry:
 	pc->ref_cnt = 1;
 	pc->mem_cgroup = mem;
 	pc->page = page;
-	pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
+	/*
+	 * If a page is accounted as a page cache, insert to inactive list.
+	 * If anon, insert to active list.
+	 */
 	if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
 		pc->flags = PAGE_CGROUP_FLAG_CACHE;
+	else
+		pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
 
 	lock_page_cgroup(page);
 	if (page_get_page_cgroup(page)) {