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

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Message-ID: <20090527004250.GA11835@sli10-desk.sh.intel.com>
Date:	Wed, 27 May 2009 08:42:50 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Kyle McMartin <kyle@...artin.ca>
Cc:	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>,
	"eric@...olt.net" <eric@...olt.net>,
	"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, 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.

Thanks,
Shaohua
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