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Date: Sat, 8 Jul 2006 17:07:03 -0700
From: Marc Singer <elf@buici.com>
To: Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: DMA memory, split_page, BUG_ON(PageCompound()), sound
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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?