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

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Date:	Tue, 28 Oct 2014 20:14:02 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Minfei Huang <mnfhuang@...il.com>, 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 10:29 AM, Thomas Gleixner wrote:
> On Tue, 28 Oct 2014, H. Peter Anvin wrote:
>> 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.
> 
> Fair enough. Then we should do that for the highmem=y case as well.
> 

It is probably even more important for highmem=y...

	-hpa


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