linux-kernel - Re: 2.6.32-rc3: low mem - only 378MB on x86

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Message-ID: <alpine.LFD.2.01.0910060722060.3432@localhost.localdomain>
Date:	Tue, 6 Oct 2009 07:26:53 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Woodhouse <dwmw2@...radead.org>
cc:	Jeff Chua <jeff.chua.linux@...il.com>, Valdis.Kletnieks@...edu,
	Tomasz Chmielewski <mangoo@...g.org>,
	Daniel J Blueman <daniel.blueman@...il.com>,
	Byron Stanoszek <bstanoszek@...time.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: 2.6.32-rc3: low mem - only 378MB on x86_32 with 64GB. Why?



On Tue, 6 Oct 2009, David Woodhouse wrote:

> On Mon, 2009-10-05 at 17:30 -0700, Linus Torvalds wrote:
> > In fact, I wish more people did that, just so that we'd get better 
> > coverage of the 32-bit compat code. We occasionally find issues there,
> > although I think it's getting rarer.
> 
> We've been running PPC64 with 32-bit userspace for a long time, so most
> of the issues with the 32-bit compat code ought to be dealt with.
> 
> There may be a few arch-specific issues for x86_64/i386, but not many.

The Intel Xorg guys used to do everything in 32-bit kernels because they 
were also testing that they didn't break compatibility (which is a big 
deal with that whole crazy DRM-in-kernel/direct-rendering-in-user-space 
thing) and seemingly didn't realize that the compat layer was _supposed_ 
to mean that they could run a 64-bit kernel and still have a working 
32-bit land.

It's driver interfaces like that that tend to break. ioctl's etc. But I 
have heard less noise about it lately, so I do think it's mostly working.

		Linus
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