linux-kernel - Re: [PATCH v2] zsmalloc: do not take class lock in zs_shrinker

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Message-ID: <20150717224233.GA7334@blaptop>
Date:	Sat, 18 Jul 2015 07:42:33 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v2] zsmalloc: do not take class lock in
 zs_shrinker_count()

Hi Sergey,

On Fri, Jul 17, 2015 at 08:18:18PM +0900, Sergey Senozhatsky wrote:
> We can avoid taking class ->lock around zs_can_compact() in
> zs_shrinker_count(), because the number that we return back
> is outdated in general case, by design. We have different
> sources that are able to change class's state right after we
> return from zs_can_compact() -- ongoing I/O operations, manually
> triggered compaction, or two of them happening simultaneously.
> 
> 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_shrinker_count() iterates them.
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

I asked to remove the comment of zs_can_compact about lock.
"Should be called under class->lock."

Otherwise,

Acked-by: Minchan Kim <minchan@...nel.org>

> ---
>  mm/zsmalloc.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 1edd8a0..ed64cf5 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1836,9 +1836,7 @@ static unsigned long zs_shrinker_count(struct shrinker *shrinker,
>  		if (class->index != i)
>  			continue;
>  
> -		spin_lock(&class->lock);
>  		pages_to_free += zs_can_compact(class);
> -		spin_unlock(&class->lock);
>  	}
>  
>  	return pages_to_free;
> -- 
> 2.4.6
> 

-- 
Kind regards,
Minchan Kim
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