Re: [Xen-devel] linux: GFP_DMA/GFP_DMA32

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 04.04.07 09:11 >>>
>How many callers rely on GFP_DMA32? We gave up on GFP_DMA because no halfway
>modern hardware relies on it and we can't currently satisfy requests for
>memory below 16MB anyway.

For GFP_DMA, I stopped counting when I found the third or fourth one - the
grep indicated another dozen or so candidates. For GFP_DMA32, it's just two
(all agp drivers, which I said I have a fix for, and 
drivers/media/video/video-buf.c -
there are many suspicious virt_to_phys() uses underneath drivers/media/, so this
subtree looks broken in general).
In may cases GFP_DMA is just being used to restrict memory to somewhere below
32-bits, not necessarily to 24.

>As for solutions, either we have to hook the memory allocator somehow to get
>a call out to allocate memory of the correct type, or callers do indeed need
>fixing one by one.

I thought about possible hooks, too, but after a page was allocated you don't
know what GFP_* it was allocated with. The only not too intrusive way I could
immediately think of would be to further leverage PG_foreign here, but I'm
afraid its use of page->index may then get into conflict with other uses...

Jan

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