linux-kernel - Re: [patch]VMSPLIT

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Message-Id: <1164962057.3299.6.camel@sli10-conroe.sh.intel.com>
Date:	Fri, 01 Dec 2006 16:34:17 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...l.org>
Subject: Re: [patch]VMSPLIT_2G conflicts with PAE

On Fri, 2006-12-01 at 08:55 +0100, Jens Axboe wrote:
> On Fri, Dec 01 2006, Shaohua Li wrote:
> > PAGE_OFFSET is 0x78000000 with VMSPLIT_2G, this address is in the middle
> > of the second pgd entry with pae enabled. This breaks assumptions
> > (address is aligned to pgd entry's address) in a lot of places like
> > pagetable_init. Fixing the assumptions is hard (eg, low mapping). SO I
> > just changed the address to 0x80000000.
> > 
> > Signed-off-by: Shaohua Li <shaohua.li@...el.com>
> > 
> > diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
> > index 8ff1c6f..fddfb26 100644
> > --- a/arch/i386/Kconfig
> > +++ b/arch/i386/Kconfig
> > @@ -532,7 +532,7 @@ endchoice
> >  config PAGE_OFFSET
> >  	hex
> >  	default 0xB0000000 if VMSPLIT_3G_OPT
> > -	default 0x78000000 if VMSPLIT_2G
> > +	default 0x80000000 if VMSPLIT_2G
> >  	default 0x40000000 if VMSPLIT_1G
> >  	default 0xC0000000
> 
> 0x78000000 was chosen since it gives you the full 2G as low memory, if
> you mave it 0x80000000 then you still have a little highmem and need
> that turned on.
Ok, Maybe the x86 relocatable patch (it seems removed the low identity
mapping) can help here. With it, we just need to fix pagetable_init.

Thanks,
Shaohua
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