From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Subject: Re: [PATCH 2/3] mm/memcg: set pos to prev unconditionally
Date: Wed, 30 Mar 2022 08:08:49 -0400
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To: Wei Yang <richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org

On Wed, Mar 30, 2022 at 12:47:50AM +0000, Wei Yang wrote:
> Something like this?
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index eed9916cdce5..5d433b79ba47 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1005,9 +1005,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>  	if (!root)
>  		root = root_mem_cgroup;
>  
> -	if (prev && !reclaim)
> -		pos = prev;
> -
>  	rcu_read_lock();
>  
>  	if (reclaim) {
> @@ -1033,6 +1030,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>  			 */
>  			(void)cmpxchg(&iter->position, pos, NULL);
>  		}
> +	} else if (prev) {
> +		pos = prev;
>  	}
>  
>  	if (pos)

Yep!