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SubjectRe: [patch 4/6] slub: avoid compiling SLAB_CACHE_DMA without DMA support
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:

#define SLUB_DMA __GFP_DMA
/* Disable DMA functionality */
#define SLUB_DMA (__force gfp_t)0

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.

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