From f59adcf5933271ab7247c4c8938c67be8905b725 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <roman.gushchin@linux.dev>
Date: Tue, 23 Jul 2024 17:12:44 +0000
Subject: [PATCH] mm: memcg: add cacheline padding after lruvec in
mem_cgroup_per_node
Oliver Sand reported a performance regression caused by commit
98c9daf5ae6b ("mm: memcg: guard memcg1-specific members of struct
mem_cgroup_per_node"), which puts some fields of the mem_cgroup_per_node
structure under the CONFIG_MEMCG_V1 config option. Apparently it causes a
false cache sharing between lruvec and lru_zone_size members of the
structure. Fix it by adding an explicit padding after the lruvec member.
Even though the padding is not required with CONFIG_MEMCG_V1 set, it seems
like the introduced memory overhead is not significant enough to warrant
another divergence in the mem_cgroup_per_node layout, so the padding is
added unconditionally.
Link: https://lkml.kernel.org/r/20240723171244.747521-1-roman.gushchin@linux.dev
Fixes: 98c9daf5ae6b ("mm: memcg: guard memcg1-specific members of struct mem_cgroup_per_node")
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202407121335.31a10cb6-oliver.sang@intel.com
Tested-by: Oliver Sang <oliver.sang@intel.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/memcontrol.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7e2eb091049a0..0e5bf25d324f0 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -109,6 +109,7 @@ struct mem_cgroup_per_node {
/* Fields which get updated often at the end. */
struct lruvec lruvec;
+ CACHELINE_PADDING(_pad2_);
unsigned long lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
struct mem_cgroup_reclaim_iter iter;
};
--
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