[PATCH 2/2] mm: memcg: add cache line padding to mem_cgroup_per_node

Roman Gushchin
2024-07-01T18:59:47Z

Memcg v1-specific fields serve a buffer function between read-mostly
and update often parts of the mem_cgroup_per_node structure.
If CONFIG_MEMCG_V1 is not set and these fields are not present,
an explicit cacheline padding is needed.

Suggested-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
include/linux/memcontrol.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 8b5b3ddeba05..60418934827c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -95,14 +95,16 @@ struct mem_cgroup_per_node {
#ifdef CONFIG_MEMCG_V1
/*
* Memcg-v1 only stuff in middle as buffer between read mostly fields
- * and update often fields to avoid false sharing. Once v1 stuff is
- * moved in a separate struct, an explicit padding is needed.
+ * and update often fields to avoid false sharing. If v1 stuff is
+ * not present, an explicit padding is needed.
*/

struct rb_node tree_node; /* RB tree node */
unsigned long usage_in_excess;/* Set to the value by which */
/* the soft limit is exceeded*/
bool on_tree;
+#else
+ CACHELINE_PADDING(_pad1_);
#endif

/* Fields which get updated often at the end. */
--
2.45.2.803.g4e1b14247a-goog