On Wed, 2009-06-03 at 11:43 -0700, Andrew Morton wrote: > On Wed, 3 Jun 2009 18:09:25 +0100 > Russell King <rmk@xxxxxxxxxxxxxxxx> wrote: > > > In > > fact, on ARM the DMA mask is exactly that - it's a 100% proper mask. It's > > not a bunch of zeros in the MSB followed by a bunch of ones down to the > > LSB. It can be a bunch of ones, a bunch of zeros, followed by a bunch of > > ones. > > > > The way we occasionally have to deal with this is to trial an allocation, > > see if the physical address fits, if not free the page and try again with > > GFP_DMA set. > > A couple of times I've suggested that we have the ability to allocate > one zone per address bit, so a 32-bit machine with 4k pages would end > up having 20 zones. Then, your funny DMA mask can be directly passed > into the page allocator as a zone mask and voila, I think. The objection I heard to that one is that the zone machinery works better with fewer zones ... but we could certainly align them along known boundaries for allocations (if it's only bit X that's the problem, say, you only need an additional zone covering that one). Based on this, I dug up the initial proposal, it was the Ottawa Kernel Summit in 2005 (I'm a packrat; I keep all my old presentations): http://www.hansenpartnership.com/sites/hansenpartnership.com/files/jejb/kernel_summit_iommu.pdf kmalloc_mask() is right at the end. It basically died for lack of interest and the fact that GFP_DMA32 satisfied 99% of the actual use cases. James -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
