linux-kernel - Re: [PATCH] x86-32: use brk segment for allocating initial kernel pagetable

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Message-ID: <86802c440902272302n3787b2bex3741b46a372a19b0@mail.gmail.com>
Date:	Fri, 27 Feb 2009 23:02:06 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH] x86-32: use brk segment for allocating initial kernel 
	pagetable

On Fri, Feb 27, 2009 at 5:51 PM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
>
> Rather than having special purpose init_pg_table_start/end variables
> to delimit the kernel pagetable built by head_32.S, just use the brk
> mechanism to extend the bss for the new pagetable.
>
> This patch removes init_pg_table_start/end and pg0, defines __brk_base
> (which is page-aligned and immediately follows _end), initializes
> the brk region to start there, and uses it for the 32-bit pagetable.
...

> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index c246dc4..ed02176 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -113,8 +113,10 @@
>  #endif
>
>  unsigned int boot_cpu_id __read_mostly;
> -__initdata unsigned long _brk_start = (unsigned long)&_end;
> -__initdata unsigned long _brk_end = (unsigned long)&_end;
> +
> +extern char __brk_base[];
> +__initdata unsigned long _brk_start = (unsigned long)__brk_base;
> +__initdata unsigned long _brk_end = (unsigned long)&__brk_base;

?

YH
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