dma-direct: add support for allocation from ZONE_DMA and ZONE_DMA32
This allows to dip into zones for lower memory if they are available.
If one of the zones is not available the corresponding GFP_* flag
will evaluate to 0 so they won't change anything. We provide an
arch tunable for those architectures that do not use GFP_DMA for
the lowest 24-bits, given that there are a few.
Roughly based on the x86 code.
Signed-off-by:
Christoph Hellwig <hch@lst.de>
parent
21f237e4