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From:   Waiman Long <longman@redhat.com>
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>
Cc:     linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
        Chris Down <chris@chrisdown.name>,
        Roman Gushchin <guro@fb.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Waiman Long <longman@redhat.com>
Subject: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max()
Date:   Sun, 13 Sep 2020 22:44:51 -0400
Message-Id: <20200914024452.19167-3-longman@redhat.com>
In-Reply-To: <20200914024452.19167-1-longman@redhat.com>
References: <20200914024452.19167-1-longman@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The mem_cgroup_get_max() function used to get memory+swap max from
both the v1 memsw and v2 memory+swap page counters & return the maximum
of these 2 values. This is redundant and it is more efficient to just
get either the v1 or the v2 values depending on which one is currently
in use.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 mm/memcontrol.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c74f1200261..ca36bed588d1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
  */
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 {
-	unsigned long max;
-
-	max = READ_ONCE(memcg->memory.max);
-	if (mem_cgroup_swappiness(memcg)) {
-		unsigned long memsw_max;
-		unsigned long swap_max;
-
-		memsw_max = memcg->memsw.max;
-		swap_max = READ_ONCE(memcg->swap.max);
-		swap_max = min(swap_max, (unsigned long)total_swap_pages);
-		max = min(max + swap_max, memsw_max);
+	unsigned long max = READ_ONCE(memcg->memory.max);
+
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
+		if (mem_cgroup_swappiness(memcg))
+			max += min(READ_ONCE(memcg->swap.max),
+				   (unsigned long)total_swap_pages);
+	} else { /* v1 */
+		if (mem_cgroup_swappiness(memcg))
+			max = memcg->memsw.max;
 	}
 	return max;
 }
-- 
2.18.1