Messages in this thread | | | Date | Sun, 09 Jul 2006 13:26:06 +1000 | From | Nick Piggin <> | Subject | Re: DMA memory, split_page, BUG_ON(PageCompound()), sound |
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Marc Singer wrote: > I'm investigating why I am triggering a BUG_ON in split_page() when I > use the sound subsystems dma memory allocation aide. > > The crux of the problem appears to be that snd_malloc_dev_pages() > passes __GFP_COMP into dma_alloc_coherent(). On the ARM and several > other architectures, the dma allocation code calls split_page () with > pages allocated with this flag which, in turn, triggers the BUG_ON() > check for the CompoundPage flag. > > So, the questions are these: Who is doing the wrong thing? Should the > snd_malloc_dev_pages() call drop the __GFP_COMP flag? Should > split_page() allow the page to be compound? Should __GFP_COMP be 0 on > ARM and other architectures that don't support compound pages?
I personally never liked the explicit __GFP_COMP going in everywhere, and would have much preferred a GFP_USERMAP, which the architecture / allocator could satisfy as they liked.
As a hack, you can make arm's dma_alloc_coherent() drop __GFP_COMP, which should work.
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