On Thu, Jul 22, 2010 at 01:43:26PM +0900, FUJITA Tomonori wrote: > On Wed, 21 Jul 2010 21:30:34 -0700 > Zach Pfeffer <zpfeffer@xxxxxxxxxxxxxx> wrote: > > > On Wed, Jul 21, 2010 at 10:44:37AM +0900, FUJITA Tomonori wrote: > > > On Tue, 20 Jul 2010 15:20:01 -0700 > > > Zach Pfeffer <zpfeffer@xxxxxxxxxxxxxx> wrote: > > > > > > > > I'm not saying that it's reasonable to pass (or even allocate) a 1MB > > > > > buffer via the DMA API. > > > > > > > > But given a bunch of large chunks of memory, is there any API that can > > > > manage them (asked this on the other thread as well)? > > > > > > What is the problem about mapping a 1MB buffer with the DMA API? > > > > > > Possibly, an IOMMU can't find space for 1MB but it's not the problem > > > of the DMA API. > > > > This goes to the nub of the issue. We need a lot of 1 MB physically > > contiguous chunks. The system is going to fragment and we'll never get > > our 12 1 MB chunks that we'll need, since the DMA API allocator uses > > the system pool it will never succeed. For this reason we reserve a > > pool of 1 MB chunks (and 16 MB, 64 KB etc...) to satisfy our > > requests. This same use case is seen on most embedded "media" engines > > that are getting built today. > > We don't need a new abstraction to reserve some memory. > > If you want pre-allocated memory pool per device (and share them with > some), the DMA API can for coherent memory (see > dma_alloc_from_coherent). You can extend the DMA API if necessary. That function won't work for us. We can't use bitmap_find_free_region(), we need to use our own allocator. If anything we need a dma_alloc_from_custom(my_allocator). Take a look at: mm: iommu: A physical allocator for the VCMM vcm_alloc_max_munch() -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>