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From: David Rientjes <rientjes@google.com>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [patch 4/6] slub: avoid compiling SLAB_CACHE_DMA without DMA support
Date: Wed, 25 May 2011 16:34:48 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.00.1105251629020.29729@chino.kir.corp.google.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1105250957180.23309@router.home>

On Wed, 25 May 2011, Christoph Lameter wrote:

> > If CONFIG_ZONE_DMA is disabled, SLAB_CACHE_DMA is a no-op.  Avoid
> > compiling support for it on such a configuration.
> 
> Setting SLAB_CACHE_DMA to zero in the !ZONE_DMA case could avoid some of
> the ifdeffery.
> 

That doesn't actually accomplish anything since all SLAB_CACHE_DMA does is 
set SLUB_DMA, which is already 0 in slub_def.h without CONFIG_ZONE_DMA:

	#ifdef CONFIG_ZONE_DMA
	#define SLUB_DMA __GFP_DMA  
	#else
	/* Disable DMA functionality */
	#define SLUB_DMA (__force gfp_t)0
	#endif

So doing the same for SLAB_CACHE_DMA wouldn't do anything.  The point of 
the patchset is to break the build if SLAB_CACHE_DMA is passed to 
kmem_cache_create() and the kernel is not compiled for DMA support.  That 
should result in a build breakage rather than silently not supporting DMA 
slab caches since it needs to be corrected at build.

  reply	other threads:[~2011-05-25 23:34 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-24 23:53 [patch 1/6] s390, block: disable fixed buffer mode when DMA support is disabled David Rientjes
2011-05-24 23:53 ` [patch 2/6] scsi: warn and avoid creating dma caches if " David Rientjes
2011-05-24 23:53 ` [patch 3/6] scsi, fnic: require DMA support for Cisco FNIC David Rientjes
2011-05-25  8:04   ` Christoph Hellwig
2011-05-25 19:28     ` Roland Dreier
2011-05-25 23:35       ` Abhijeet Joglekar (abjoglek)
2011-05-25 23:35         ` Abhijeet Joglekar (abjoglek)
2011-05-25 23:40         ` David Rientjes
2011-05-24 23:53 ` [patch 4/6] slub: avoid compiling SLAB_CACHE_DMA without DMA support David Rientjes
2011-05-25 14:58   ` Christoph Lameter
2011-05-25 23:34     ` David Rientjes [this message]
2011-05-24 23:53 ` [patch 5/6] slab: " David Rientjes
2011-05-24 23:53 ` [patch 6/6] slab: only define SLAB_CACHE_DMA for CONFIG_ZONE_DMA David Rientjes
2011-05-25 10:49   ` Heiko Carstens
2011-05-25 15:02     ` Christoph Lameter
2011-05-25 23:37     ` David Rientjes
2011-05-25  7:24 ` [patch 1/6] s390, block: disable fixed buffer mode when DMA support is disabled Heiko Carstens

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