linux-kernel - [PATCH 2/2] mm: memcg: add cache line padding to mem_cgroup_per

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Date: Mon,  1 Jul 2024 18:59:32 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Roman Gushchin <roman.gushchin@...ux.dev>
Subject: [PATCH 2/2] mm: memcg: add cache line padding to mem_cgroup_per_node

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@...ux.dev>
Signed-off-by: Roman Gushchin <roman.gushchin@...ux.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