Re: DMA memory, split_page, BUG_ON(PageCompound()), sound

[Nick Piggin]

Takashi Iwai wrote:
> At Wed, 12 Jul 2006 11:32:41 +0100,

> > In which case should ALSA be passing __GFP_COMP to the dma allocator ?

Yes, sorry I didn't answer your question: ALSA basically wants to be
able to have that memory mmapable by userspace programs, and it doesn't
care whether this is via compound pages or split pages.

> I would be willing to remove __GFP_COMP if it's not needed :)
> Passing this flag is really confusing.  The driver doesn't use the
> compound pages at all but it was added just to enable mmap support.
> So, Nick's proposal appears reasonable to me.

I don't think it would be hard. Just need a bit of thinking about how
to go about composing some sort of GFP_USERMAP that can easily be
handled by all allocators, without costing performance or being too
intrusive.

I suspect I won't have time to wade into such an exercise until after
OLS. But I could give a quick review for anyone who does ;)

--
SUSE Labs, Novell Inc.
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