linux-kernel - [PATCH v3 2/3] mm/memcg: Simplify mem_cgroup_get

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Date:   Mon, 14 Sep 2020 10:19:55 -0400
From:   Waiman Long <longman@...hat.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Shakeel Butt <shakeelb@...gle.com>,
        Chris Down <chris@...isdown.name>,
        Roman Gushchin <guro@...com>,
        Yafang Shao <laoar.shao@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v3 2/3] mm/memcg: Simplify mem_cgroup_get_max()

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@...hat.com>
---
 mm/memcontrol.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c74f1200261..2331d4bc7c4d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1633,17 +1633,19 @@ 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)) {
+			unsigned long memsw = READ_ONCE(memcg->memsw.max);
+
+			if (memsw > max)
+				max += min(memsw - max, (unsigned long)total_swap_pages);
+		}
 	}
 	return max;
 }
-- 
2.18.1