linux-kernel - Re: [PATCH] mm: memcg: add cacheline padding after lruvec in mem_cgroup_per

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Message-ID: <4xrfzyqmmq5gmowvyxxqn2xogo4o3rktc2btces3zeamhnaoxz@kor2cgbm46ou>
Date: Tue, 23 Jul 2024 10:30:31 -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>, 
	kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH] mm: memcg: add cacheline padding after lruvec in
 mem_cgroup_per_node

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@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202407121335.31a10cb6-oliver.sang@intel.com
> Tested-by: Oliver Sang <oliver.sang@...el.com>
> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>

Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>