linux-kernel - Re: [PATCH RFC] x86: add brk allocation for very, very early allocations

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Date:	Fri, 27 Feb 2009 11:26:53 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] x86: add brk allocation for very, very early allocations

H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>   
>> unsigned int boot_cpu_id __read_mostly;
>> +__initdata unsigned long _brk_start, _brk_end;
>>
>>     
>
> Better yet, initialize _brk_start and _brk_end statically:
>
> extern const char _end[];
> __initdata unsigned long _brk_start = (unsigned long)&_end;
> __initdata unsigned long _brk_end   = (unsigned long)&_end;
>
> That way it's available from the first instruction, and we can fully
> remove the x86-32 init_pg_tables_end and replace it with _brk_end (thus
> putting the initial page tables in the brk.)

Yes.  It doesn't work for Xen (the domain builder puts the initrd and 
Xen-built pagetable immediately after the kernel's bss), but its no 
problem to move the brk in that case.

    J
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