Re: [Patch v2 3/3] mm/memcg: move generation assignment and comparison together

[Roman Gushchin <roman.gushchin@linux.dev>]

On Wed, Mar 30, 2022 at 11:47:19PM +0000, Wei Yang wrote:
> For each round-trip, we assign generation on first invocation and
> compare it on subsequent invocations.
> 
> Let's move them together to make it more self-explaining. Also this
> reduce a check on prev.
> 
> [hannes@cmpxchg.org: better comment to explain reclaim model]
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>

> 
> ---
> v2: a better comment from Johannes
> ---
>  mm/memcontrol.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5d433b79ba47..2cd8bfdec379 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1013,7 +1013,13 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>  		mz = root->nodeinfo[reclaim->pgdat->node_id];
>  		iter = &mz->iter;
>  
> -		if (prev && reclaim->generation != iter->generation)
> +		/*
> +		 * On start, join the current reclaim iteration cycle.
> +		 * Exit when a concurrent walker completes it.
> +		 */
> +		if (!prev)
> +			reclaim->generation = iter->generation;
> +		else if (reclaim->generation != iter->generation)
>  			goto out_unlock;
>  
>  		while (1) {
> @@ -1075,8 +1081,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>  
>  		if (!memcg)
>  			iter->generation++;
> -		else if (!prev)
> -			reclaim->generation = iter->generation;
>  	}
>  
>  out_unlock:
> -- 
> 2.33.1
> 
>