linux-kernel - Re: [PATCH 2/5] mm/slub: query dynamic DEBUG

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Date:	Thu, 4 Feb 2016 09:31:14 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Joonsoo Kim <js1304@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Takashi Iwai <tiwai@...e.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Christoph Lameter <cl@...ux.com>, linux-api@...r.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 2/5] mm/slub: query dynamic DEBUG_PAGEALLOC setting

On 02/04/2016 06:56 AM, Joonsoo Kim wrote:
> We can disable debug_pagealloc processing even if the code is complied
> with CONFIG_DEBUG_PAGEALLOC. This patch changes the code to query
> whether it is enabled or not in runtime.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>  mm/slub.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 7d4da68..7b5a965 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -256,11 +256,12 @@ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
>  {
>  	void *p;
> 
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
> -#else
> -	p = get_freepointer(s, object);
> -#endif
> +	if (debug_pagealloc_enabled()) {
> +		probe_kernel_read(&p,
> +			(void **)(object + s->offset), sizeof(p));

Hmm, this might be a good case for a line longer than 80 chars....

As an alternative revert the logic and return early:


	if (!debug_pagealloc_enabled())
		return get_freepointer(s, object);
	probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
	return p;

?


> +	} else
> +		p = get_freepointer(s, object);
> +
>  	return p;
>  }
>