Subject: Re: mm/slab.c: remove effectively dead code from kmem_cache_create
From: Pekka Enberg <penberg@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: daniel.santos@pobox.com, Daniel Santos <danielfsantos@att.net>,
        torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
In-Reply-To: <20120209143924.886e0ff6.akpm@linux-foundation.org>
References: <4F334897.5010405@att.net>
	 <20120209143924.886e0ff6.akpm@linux-foundation.org>
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Date: Fri, 10 Feb 2012 15:06:41 +0200
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On Thu, 2012-02-09 at 14:39 -0800, Andrew Morton wrote:
> kmem_cache_create() is called extremely rarely, so the performance
> benefit here is negligible.
> 
> We could presumably avoid two of those ifdefs by defining SLAB_RED_ZONE
> and SLAB_STORE_USER to be zero if !defined(DEBUG).  Personally I think
> that's a bit too subtle and would prefer the explicit ifdefs.
> 
> In my x86_64 allnoconfig build the patch reduces slab.o's text size
> from 12859 bytes to 12812.  I'll let Pekka decide if that's worth it ;)

The text savings are worth it but I'd really prefer to see
include/linux/slab.h patched to define debugging flags as zero for
non-CONFIG_SLAB_DEBUG and let GCC eliminate the dead code for us.

			Pekka

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