memcg: reduce function dereference

This function dereferences res far too often, so optimize it.
Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Jeff Liu <jeff.liu@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/res_counter.c

@@ -178,27 +178,30 @@ u64 res_counter_read_u64(struct res_counter *counter, int member)
 #endif
 
 int res_counter_memparse_write_strategy(const char *buf,
-					unsigned long long *res)
+					unsigned long long *resp)
 {
 	char *end;
+	unsigned long long res;
 
 	/* return RES_COUNTER_MAX(unlimited) if "-1" is specified */
 	if (*buf == '-') {
-		*res = simple_strtoull(buf + 1, &end, 10);
-		if (*res != 1 || *end != '\0')
+		res = simple_strtoull(buf + 1, &end, 10);
+		if (res != 1 || *end != '\0')
 			return -EINVAL;
-		*res = RES_COUNTER_MAX;
+		*resp = RES_COUNTER_MAX;
 		return 0;
 	}
 
-	*res = memparse(buf, &end);
+	res = memparse(buf, &end);
 	if (*end != '\0')
 		return -EINVAL;
 
-	if (PAGE_ALIGN(*res) >= *res)
-		*res = PAGE_ALIGN(*res);
+	if (PAGE_ALIGN(res) >= res)
+		res = PAGE_ALIGN(res);
 	else
-		*res = RES_COUNTER_MAX;
+		res = RES_COUNTER_MAX;
+
+	*resp = res;
 
 	return 0;
 }