linux-kernel - Re: [PATCH] drm: i915: ensure objects are allocated below 4GB on PAE

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Message-Id: <1243446012.8400.37.camel@gaiman.anholt.net>
Date:	Wed, 27 May 2009 10:40:12 -0700
From:	Eric Anholt <eric@...olt.net>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Kyle McMartin <kyle@...artin.ca>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	"airlied@...hat.com" <airlied@...hat.com>,
	"dri-devel@...ts.sf.net" <dri-devel@...ts.sf.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"stable@...nel.org" <stable@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] drm: i915: ensure objects are allocated below 4GB on
 PAE

On Wed, 2009-05-27 at 08:42 +0800, Shaohua Li wrote:
> 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.

Those 945Gs don't have memory located above 4G, from my reading of the
chipset specs.

-- 
Eric Anholt
eric@...olt.net                         eric.anholt@...el.com



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