The patch titled
Subject: mm: memcg: add cacheline padding after lruvec in mem_cgroup_per_node
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-memcg-add-cacheline-padding-after-lruvec-in-mem_cgroup_per_node.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-add-cacheline-padding-after-lruvec-in-mem_cgroup_per_node.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Subject: mm: memcg: add cacheline padding after lruvec in mem_cgroup_per_node
Date: Tue, 23 Jul 2024 17:12:44 +0000
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@xxxxxxxxx
Fixes: 98c9daf5ae6b ("mm: memcg: guard memcg1-specific members of struct mem_cgroup_per_node")
Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202407121335.31a10cb6-oliver.sang@xxxxxxxxx
Tested-by: Oliver Sang <oliver.sang@xxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 1 +
1 file changed, 1 insertion(+)
--- a/include/linux/memcontrol.h~mm-memcg-add-cacheline-padding-after-lruvec-in-mem_cgroup_per_node
+++ a/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;
};
_
Patches currently in -mm which might be from roman.gushchin@xxxxxxxxx are
mm-memcg-add-cacheline-padding-after-lruvec-in-mem_cgroup_per_node.patch
