linux-kernel - Re: GFP_DMA32 and PAE x86 machines

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Message-Id: <200705311411.39764.ak@suse.de>
Date:	Thu, 31 May 2007 14:11:39 +0200
From:	Andi Kleen <ak@...e.de>
To:	"Dave Airlie" <airlied@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"Linus Torvalds" <torvalds@...l.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: GFP_DMA32 and PAE x86 machines

> Funnily enough I have just today with an app I have which uses 1.2GB
> of textures :-)

Realistic app which is something users really run?
Also do the other constraints above apply?

If you use pci_alloc_coherent() then it will already take care of the rules
above btw (e.g. DTRT when the machine has <3GB etc.) 

> we are currently using GFP_DMA32 in the TTM allocator code, however
> what I really want on x86 non-PAE is GFP_HIGHMEM (as DMA32 does
> nothing) however on x86-PAE I don't want that I want a real GFP_DMA32,
> and on x86-64 I want the current GFP_DMA32,

You should be probably using pci_alloc_coherent() at least on x86.
It might get more expensive on some obscure platforms (which DRM
likely doesn't support anyways), but if it does perhaps a pci_alloc_noncoherent()
or so would be useful (on x86 it would be the same) 

-Andi
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