[patch 083/181] mm/memcg: simplify mem_cgroup_get_max()

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From: Waiman Long <longman@xxxxxxxxxx>
Subject: mm/memcg: simplify mem_cgroup_get_max()

mem_cgroup_get_max() 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.

[longman@xxxxxxxxxx: v4]
  Link: https://lkml.kernel.org/r/20200914150928.7841-1-longman@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20200914024452.19167-3-longman@xxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memcontrol.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

--- a/mm/memcontrol.c~mm-memcg-simplify-mem_cgroup_get_max
+++ a/mm/memcontrol.c
@@ -1633,17 +1633,19 @@ void mem_cgroup_print_oom_meminfo(struct
  */
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 {
-	unsigned long max;
+	unsigned long max = READ_ONCE(memcg->memory.max);
 
-	max = READ_ONCE(memcg->memory.max);
-	if (mem_cgroup_swappiness(memcg)) {
-		unsigned long memsw_max;
-		unsigned long swap_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)) {
+			/* Calculate swap excess capacity from memsw limit */
+			unsigned long swap = READ_ONCE(memcg->memsw.max) - 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);
+			max += min(swap, (unsigned long)total_swap_pages);
+		}
 	}
 	return max;
 }
_



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