linux-kernel - Re: [PATCH v2 2/4] mm: clean up validate

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Date:   Thu, 12 Sep 2019 12:46:23 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] mm: clean up validate_slab()

On Wed, Sep 11, 2019 at 08:31:09PM -0600, Yu Zhao wrote:
> The function doesn't need to return any value, and the check can be
> done in one pass.
> 
> There is a behavior change: before the patch, we stop at the first
> invalid free object; after the patch, we stop at the first invalid
> object, free or in use. This shouldn't matter because the original
> behavior isn't intended anyway.
> 
> Signed-off-by: Yu Zhao <yuzhao@...gle.com>
> ---
>  mm/slub.c | 21 ++++++++-------------
>  1 file changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 62053ceb4464..7b7e1ee264ef 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4386,31 +4386,26 @@ static int count_total(struct page *page)
>  #endif
>  
>  #ifdef CONFIG_SLUB_DEBUG
> -static int validate_slab(struct kmem_cache *s, struct page *page,
> +static void validate_slab(struct kmem_cache *s, struct page *page,
>  						unsigned long *map)
>  {
>  	void *p;
>  	void *addr = page_address(page);
>  
> -	if (!check_slab(s, page) ||
> -			!on_freelist(s, page, NULL))
> -		return 0;
> +	if (!check_slab(s, page) || !on_freelist(s, page, NULL))
> +		return;
>  
>  	/* Now we know that a valid freelist exists */
>  	bitmap_zero(map, page->objects);
>  
>  	get_map(s, page, map);
>  	for_each_object(p, s, addr, page->objects) {
> -		if (test_bit(slab_index(p, s, addr), map))
> -			if (!check_object(s, page, p, SLUB_RED_INACTIVE))
> -				return 0;
> -	}
> +		u8 val = test_bit(slab_index(p, s, addr), map) ?
> +			 SLUB_RED_INACTIVE : SLUB_RED_ACTIVE;

Proper 'if' would be more readable.

Other than that look fine to me.

>  
> -	for_each_object(p, s, addr, page->objects)
> -		if (!test_bit(slab_index(p, s, addr), map))
> -			if (!check_object(s, page, p, SLUB_RED_ACTIVE))
> -				return 0;
> -	return 1;
> +		if (!check_object(s, page, p, val))
> +			break;
> +	}
>  }
>  
>  static void validate_slab_slab(struct kmem_cache *s, struct page *page,
> -- 
> 2.23.0.162.g0b9fbb3734-goog
> 

-- 
 Kirill A. Shutemov