linux-kernel - Re: [PATCH] slab: add missing guard for kernel_map

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Message-ID: <20090522101733.GA12967@homer.shelbyville.oz>
Date:	Fri, 22 May 2009 19:47:33 +0930
From:	Ron <ron@...ian.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	cl@...ux-foundation.org, mpm@...enic.com, linux-mm@...ck.org,
	akinobu.mita@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: add missing guard for kernel_map_pages() use

On Fri, May 22, 2009 at 06:20:40PM +0930, Ron wrote:
> 
> All other uses of kernel_map_pages() are explicitly excluded without
> CONFIG_DEBUG_PAGEALLOC, this one should be too.
> 
> Signed-off-by: Ron Lee <ron@...ian.org>
> 
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 9a90b00..b5e5b27 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2674,10 +2683,12 @@ static void cache_init_objs(struct kmem_cache *cachep,
>  				slab_error(cachep, "constructor overwrote the"
>  					   " start of an object");
>  		}
> +#ifdef CONFIG_DEBUG_PAGEALLOC
>  		if ((cachep->buffer_size % PAGE_SIZE) == 0 &&
>  			    OFF_SLAB(cachep) && cachep->flags & SLAB_POISON)
>  			kernel_map_pages(virt_to_page(objp),
>  					 cachep->buffer_size / PAGE_SIZE, 0);
> +#endif
>  #else
>  		if (cachep->ctor)
>  			cachep->ctor(objp);

Actually, no.  I'm wrong on this one.  The compiler will already take that
one away because kernel_map_pages() is an empty function in that case.

It's subtle, but this extra guard actually adds nothing (unless you consider
more #ifdefs to be 'clarifying');

Sorry for the extra noise,
Ron


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