linux-kernel - Re: [PATCH] mm: Avoid overlap the fixmap area on i386

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Date:	Tue, 28 Oct 2014 10:24:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Minfei Huang <mnfhuang@...il.com>
CC:	mingo@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Avoid overlap the fixmap area on i386

On 10/28/2014 04:06 AM, Thomas Gleixner wrote:
>>
>> The available address we can use is lower than FIXADDR_BOOT_START. So
>> We will set the kmap boundary below the FIXADDR_BOOT_START, if configure
>> the high memory.
>>
>> If we configure the high memory, the vmalloc reserve area should end
>> up to PKMAP_BASE, otherwise should end up to FIXADDR_BOOT_START.
> 
> Which is not really a problem, because the FIXADDR_BOOT area is only
> used during boot for early_ioremap() and it's unused when ioremap() is
> functional. vmalloc becomes available after early boot so the
> FIXADDR_BOOT area is available for reuse.
> 

Given the very limited address space available on i386, it would be
extremely undesirable to not reuse address space when possible.

	-hpa

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