linux-kernel - Re: [PATCH 3/3] zsmalloc: do not take class lock in zs_pages_to

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Message-ID: <20150715040703.GA545@swordfish>
Date:	Wed, 15 Jul 2015 13:07:03 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 3/3] zsmalloc: do not take class lock in
 zs_pages_to_compact()

On (07/11/15 18:45), Sergey Senozhatsky wrote:
[..]
> We re-do this calculations during compaction on a per class basis
> anyway.
> 
> zs_unregister_shrinker() will not return until we have an active
> shrinker, so classes won't unexpectedly disappear while
> zs_pages_to_compact(), invoked by zs_shrinker_count(), iterates
> them.
> 
> When called from zram, we are protected by zram's ->init_lock,
> so, again, classes will be there until zs_pages_to_compact()
> iterates them.
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> ---
>  mm/zsmalloc.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index b10a228..824c182 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1811,9 +1811,7 @@ unsigned long zs_pages_to_compact(struct zs_pool *pool)
>  		if (class->index != i)
>  			continue;
>  
> -		spin_lock(&class->lock);
>  		pages_to_free += zs_can_compact(class);
> -		spin_unlock(&class->lock);
>  	}
>  
>  	return pages_to_free;

This patch still makes sense. Agree?

	-ss
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