On Wed, Nov 5, 2014 at 12:18 PM, Gregory Fong <gregory.0xf0@xxxxxxxxx> wrote: > On Tue, Nov 4, 2014 at 2:27 PM, Michal Nazarewicz <mina86@xxxxxxxxxx> wrote: >> On Tue, Nov 04 2014, Gregory Fong wrote: >>> The alignment in cma_alloc() is done w.r.t. the bitmap. This is a >>> problem when, for example: >>> >>> - a device requires 16M (order 12) alignment >>> - the CMA region is not 16 M aligned I think the device driver should ensure that situation could not occur, by assign suitable alignment parameter in cma_declare_contiguous(). >>> In such a case, can result with the CMA region starting at, say, >>> 0x2f800000 but any allocation you make from there will be aligned from >>> there. Requesting an allocation of 32 M with 16 M alignment, will >>> result in an allocation from 0x2f800000 to 0x31800000, which doesn't >>> work very well if your strange device requires 16M alignment. >>> >>> This doesn't have the behavior I would expect, which would be for the >>> allocation to be aligned w.r.t. the start of memory. I realize that >>> aligning the CMA region is an option, but don't see why cma_alloc() >>> aligns to the start of the CMA region. Is there a good reason for >>> having cma_alloc() alignment work this way? >> >> No, it's a bug. The alignment should indicate alignment of physical >> address not position in CMA region. >> > > Ah, now I see that Marek submitted this patch from you back in 2011 > that would have allowed the bitmap lib to support an alignment offset: > http://thread.gmane.org/gmane.linux.kernel/1121103/focus=1121100 > > Any idea why this didn't make it into the later changesets? If not, > I'll resubmit it and to use it to fix this bug. > > Thanks, > Gregory > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>