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Date: Thu, 15 Nov 2012 11:28:00 -0800
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Subject: Re: [PATCH 21/46] x86, mm: setup page table in top-down
From: Yinghai Lu <yinghai@kernel.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        Jacob Shin <jacob.shin@amd.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Tue, Nov 13, 2012 at 12:36 PM, Yinghai Lu <yinghai@kernel.org> wrote:
> On Tue, Nov 13, 2012 at 12:01 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 11/13/2012 11:59 AM, Yinghai Lu wrote:
>>>>
>>>> The changes to init_mem_mapping are a bit iffy but they aren't too
>>>> unreasonable.
>>>> Overall the patch is OK even though I would certainly appreciate more
>>>> comments and better variable names (real_end?), see below.
>>>
>>> real_end is not good?
>>>
>>> xen put big reserved range between real_end and end.
>>>
>>> that real_end is some kind of end of real usable areas.
>>>
>>> so change to real_usable_end  or usable_end?
>>>
>>
>> A description of a variable that includes the words "some kind of"
>> clearly indicates major confusion.  We need to know what the semantics
>> are, here.
>
> originally, we map range in this sequence:
> 1. map [0, 1M],
> 2. map 2M near max_pfn. and end is max_pfn<<PAGE_SHIFT
> 3. use new mapped area, to map low range.
> 4. change step size if more ram get mapped.
> 5. goto 3, until reach 1M.
>
> now for xen, there is big chunk range under max_pfn and they are reserved
> in memblock.reserved.
> so even we map them, we still can not use them for page table.
>
> so 2 become:
> 2a. find real_end under max_pfn that we can use it for page table
> 2b, map [real_end - 2M, real_end)
>
> and need to add
> 6. map [real_end, max_pfn<<PAGE_SHIFT)

hi, peter,

I updated for-x86-mm branch at
	git://git.kernel.org/pub/scm/linux/kernel/git/yinghai/linux-yinghai.git
for-x86-mm

with updated changlog and acked-by from Stefano for some patches.