Re: [PATCH] drm: i915: ensure objects are allocated below 4GB onPAE

From: Shaohua Li
Date: Tue May 26 2009 - 20:43:03 EST

On Wed, May 27, 2009 at 08:18:40AM +0800, Kyle McMartin wrote:
> On Tue, May 26, 2009 at 11:55:50PM +0100, Hugh Dickins wrote:
> > I'm confused: I thought GFP_DMA32 only applies on x86_64:
> > my 32-bit PAE machine with (slightly!) > 4GB shows no ZONE_DMA32.
> > Does this patch perhaps depend on another, to enable DMA32 on 32-bit
> > PAE, or am I just in a muddle?
> >
> No, you're exactly right, I'm just a muppet and missed the obvious.
> Looks like the "correct" fix is the fact that the allocation is thus
> filled out with GFP_USER, therefore, from ZONE_NORMAL, and below
> max_low_pfn.
> Looks like we'll need some additional thinking to get true ZONE_DMA32 on
> i386... ugh, I'll look into it tonight.
For i386, GFP_USER is enough. But 945G GART can only map to physical page < 4G,
so for x64, we need GFP_DMA32. This is the reason I add extra GFP_DMA32.

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