Re: [PATCH 0/6] memcg: group struct fields by access pattern

[Andrew Morton]

On Fri,  4 Sep 2026 20:05:16 -0700 Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote:

> Every so often we get a memcg performance regression caused by nothing
> more than a field moving. Someone adds a field, removes one, or puts a
> few behind a config option. The layout shifts, fields with different
> access patterns land on the same cache line, and a bot reports a
> regression.
> 
> ...
>
> This series makes the layout a contract the compiler checks, the same
> way struct net_device does it. Fields are sorted into named cache line
> groups by access pattern, and memcg_struct_check() verifies at build
> time that every field sits in its group. A field added in the wrong
> place now breaks the build instead of quietly costing a few percent.

Sounds smart.

Significant repair work was needed for the struct mem_cgroup_per_node
and struct mem_cgroup alterations, due to the below pending changes.  I
think I got it all, please check.

--- linux-7.3-rc1/include/linux/memcontrol.h	2026-08-30 04:44:06.000000000 -0700
+++ 25/include/linux/memcontrol.h	2026-09-05 16:31:03.119571612 -0700
@@ -95,25 +95,12 @@ struct mem_cgroup_per_node {
 	struct lruvec_stats			*lruvec_stats;
 	struct shrinker_info __rcu	*shrinker_info;
 
-#ifdef CONFIG_MEMCG_V1
-	/*
-	 * Memcg-v1 only stuff in middle as buffer between read mostly fields
-	 * 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. */
 	struct lruvec		lruvec;
 	CACHELINE_PADDING(_pad2_);
-	unsigned long		lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
+	long			lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
 	struct mem_cgroup_reclaim_iter	iter;
 
 	/*
@@ -293,8 +280,6 @@ struct mem_cgroup {
 
 	struct memcg1_events_percpu __percpu *events_percpu;
 
-	unsigned long soft_limit;
-
 	/* protected by memcg_oom_lock */
 	bool oom_lock;
 	int under_oom;