memcg: convert uncharge batching from bytes to page granularity

We never uncharge subpage quantities.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/sched.h

@@ -1524,8 +1524,8 @@ struct task_struct {
 	struct memcg_batch_info {
 		int do_batch;	/* incremented when batch uncharge started */
 		struct mem_cgroup *memcg; /* target memcg of uncharge */
-		unsigned long bytes; 		/* uncharged usage */
-		unsigned long memsw_bytes; /* uncharged mem+swap usage */
+		unsigned long nr_pages;	/* uncharged usage */
+		unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
 	} memcg_batch;
 #endif
 };

mm/memcontrol.c

@@ -2579,9 +2579,9 @@ __do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype,
 	if (batch->memcg != mem)
 		goto direct_uncharge;
 	/* remember freed charge and uncharge it later */
-	batch->bytes += PAGE_SIZE;
+	batch->nr_pages++;
 	if (uncharge_memsw)
-		batch->memsw_bytes += PAGE_SIZE;
+		batch->memsw_nr_pages++;
 	return;
 direct_uncharge:
 	res_counter_uncharge(&mem->res, page_size);
@@ -2708,8 +2708,8 @@ void mem_cgroup_uncharge_start(void)
 	/* We can do nest. */
 	if (current->memcg_batch.do_batch == 1) {
 		current->memcg_batch.memcg = NULL;
-		current->memcg_batch.bytes = 0;
-		current->memcg_batch.memsw_bytes = 0;
+		current->memcg_batch.nr_pages = 0;
+		current->memcg_batch.memsw_nr_pages = 0;
 	}
 }
 
@@ -2730,10 +2730,12 @@ void mem_cgroup_uncharge_end(void)
 	 * This "batch->memcg" is valid without any css_get/put etc...
 	 * bacause we hide charges behind us.
 	 */
-	if (batch->bytes)
-		res_counter_uncharge(&batch->memcg->res, batch->bytes);
-	if (batch->memsw_bytes)
-		res_counter_uncharge(&batch->memcg->memsw, batch->memsw_bytes);
+	if (batch->nr_pages)
+		res_counter_uncharge(&batch->memcg->res,
+				     batch->nr_pages * PAGE_SIZE);
+	if (batch->memsw_nr_pages)
+		res_counter_uncharge(&batch->memcg->memsw,
+				     batch->memsw_nr_pages * PAGE_SIZE);
 	memcg_oom_recover(batch->memcg);
 	/* forget this pointer (for sanity check) */
 	batch->memcg = NULL;