| Message ID | 20240723171244.747521-1-roman.gushchin@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: memcg: add cacheline padding after lruvec in mem_cgroup_per_node | expand |
On Tue, Jul 23, 2024 at 05:12:44PM GMT, Roman Gushchin wrote: > Oliver Sand Oliver Sang > 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. > > Fixes: 98c9daf5ae6b ("mm: memcg: guard memcg1-specific members of struct mem_cgroup_per_node") > 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> > Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 7e2eb091049a..0e5bf25d324f 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; };
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. Fixes: 98c9daf5ae6b ("mm: memcg: guard memcg1-specific members of struct mem_cgroup_per_node") 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> Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev> --- include/linux/memcontrol.h | 1 + 1 file changed, 1 insertion(+)