linux-kernel - Re: [PATCH v1 7/9] mm: memcg: guard memcg1-specific members of struct mem_cgroup_per

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Date: Fri, 28 Jun 2024 17:52:33 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 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>
Subject: Re: [PATCH v1 7/9] mm: memcg: guard memcg1-specific members of
 struct mem_cgroup_per_node

On Fri, Jun 28, 2024 at 09:03:15PM GMT, Roman Gushchin wrote:
> Put memcg1-specific members of struct mem_cgroup_per_node under the
> CONFIG_MEMCG_V1 config option.
> 
> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> ---
>  include/linux/memcontrol.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 107b0c5d6eab..c7ef628ee882 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -92,6 +92,7 @@ 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. Once v1 stuff is
> @@ -102,6 +103,7 @@ struct mem_cgroup_per_node {
>  	unsigned long		usage_in_excess;/* Set to the value by which */
>  						/* the soft limit is exceeded*/
>  	bool			on_tree;

Here we definitely need a padding after the pointers and before the
lruvec. We can add a #else to the #ifdef CONFIG_MEMCG_V1 and put a
cacheline padding in it.

> +#endif
>  
>  	/* Fields which get updated often at the end. */
>  	struct lruvec		lruvec;
> -- 
> 2.45.2.803.g4e1b14247a-goog
>