memcg: refactor mem_cgroup_resize_limit()

mem_cgroup_resize_limit() and mem_cgroup_resize_memsw_limit() have
identical logics.  Refactor code so we don't need to keep two pieces of
code that does same thing.

Link: http://lkml.kernel.org/r/20180108224238.14583-1-yuzhao@google.comSigned-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2461,13 +2461,15 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
 static DEFINE_MUTEX(memcg_limit_mutex);
 
 static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
-				   unsigned long limit)
+				   unsigned long limit, bool memsw)
 {
 	unsigned long curusage;
 	unsigned long oldusage;
 	bool enlarge = false;
 	int retry_count;
 	int ret;
+	bool limits_invariant;
+	struct page_counter *counter = memsw ? &memcg->memsw : &memcg->memory;
 
 	/*
 	 * For keeping hierarchical_reclaim simple, how long we should retry
@@ -2477,58 +2479,7 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
 	retry_count = MEM_CGROUP_RECLAIM_RETRIES *
 		      mem_cgroup_count_children(memcg);
 
-	oldusage = page_counter_read(&memcg->memory);
-
-	do {
-		if (signal_pending(current)) {
-			ret = -EINTR;
-			break;
-		}
-
-		mutex_lock(&memcg_limit_mutex);
-		if (limit > memcg->memsw.limit) {
-			mutex_unlock(&memcg_limit_mutex);
-			ret = -EINVAL;
-			break;
-		}
-		if (limit > memcg->memory.limit)
-			enlarge = true;
-		ret = page_counter_limit(&memcg->memory, limit);
-		mutex_unlock(&memcg_limit_mutex);
-
-		if (!ret)
-			break;
-
-		try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, true);
-
-		curusage = page_counter_read(&memcg->memory);
-		/* Usage is reduced ? */
-		if (curusage >= oldusage)
-			retry_count--;
-		else
-			oldusage = curusage;
-	} while (retry_count);
-
-	if (!ret && enlarge)
-		memcg_oom_recover(memcg);
-
-	return ret;
-}
-
-static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
-					 unsigned long limit)
-{
-	unsigned long curusage;
-	unsigned long oldusage;
-	bool enlarge = false;
-	int retry_count;
-	int ret;
-
-	/* see mem_cgroup_resize_res_limit */
-	retry_count = MEM_CGROUP_RECLAIM_RETRIES *
-		      mem_cgroup_count_children(memcg);
-
-	oldusage = page_counter_read(&memcg->memsw);
+	oldusage = page_counter_read(counter);
 
 	do {
 		if (signal_pending(current)) {
@@ -2537,22 +2488,28 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
 		}
 
 		mutex_lock(&memcg_limit_mutex);
-		if (limit < memcg->memory.limit) {
+		/*
+		 * Make sure that the new limit (memsw or memory limit) doesn't
+		 * break our basic invariant rule memory.limit <= memsw.limit.
+		 */
+		limits_invariant = memsw ? limit >= memcg->memory.limit :
+					   limit <= memcg->memsw.limit;
+		if (!limits_invariant) {
 			mutex_unlock(&memcg_limit_mutex);
 			ret = -EINVAL;
 			break;
 		}
-		if (limit > memcg->memsw.limit)
+		if (limit > counter->limit)
 			enlarge = true;
-		ret = page_counter_limit(&memcg->memsw, limit);
+		ret = page_counter_limit(counter, limit);
 		mutex_unlock(&memcg_limit_mutex);
 
 		if (!ret)
 			break;
 
-		try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, false);
+		try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, !memsw);
 
-		curusage = page_counter_read(&memcg->memsw);
+		curusage = page_counter_read(counter);
 		/* Usage is reduced ? */
 		if (curusage >= oldusage)
 			retry_count--;
@@ -3014,10 +2971,10 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
 		}
 		switch (MEMFILE_TYPE(of_cft(of)->private)) {
 		case _MEM:
-			ret = mem_cgroup_resize_limit(memcg, nr_pages);
+			ret = mem_cgroup_resize_limit(memcg, nr_pages, false);
 			break;
 		case _MEMSWAP:
-			ret = mem_cgroup_resize_memsw_limit(memcg, nr_pages);
+			ret = mem_cgroup_resize_limit(memcg, nr_pages, true);
 			break;
 		case _KMEM:
 			ret = memcg_update_kmem_limit(memcg, nr_pages);