linux-kernel - Re: [PATCH 21/46] x86, mm: setup page table in top-down

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Message-ID: <CAE9FiQU1HGyw8ZLu8KdmR3ikyZ=YTG+8dUoDAVbO4Bc1hEPPgQ@mail.gmail.com>
Date:	Tue, 13 Nov 2012 11:59:40 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, Jacob Shin <jacob.shin@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 21/46] x86, mm: setup page table in top-down

On Tue, Nov 13, 2012 at 9:26 AM, Stefano Stabellini
<stefano.stabellini@...citrix.com> wrote:
> On Mon, 12 Nov 2012, Yinghai Lu wrote:
>> Get pgt_buf early from BRK, and use it to map PMD_SIZE from top at first.
>> Then use mapped pages to map more ranges below, and keep looping until
>> all pages get mapped.
>>
>> alloc_low_page will use page from BRK at first, after that buffer is used
>> up, will use memblock to find and reserve pages for page table usage.
>>
>> Introduce min_pfn_mapped to make sure find new pages from mapped ranges,
>> that will be updated when lower pages get mapped.
>>
>> Also add step_size to make sure that don't try to map too big range with
>> limited mapped pages initially, and increase the step_size when we have
>> more mapped pages on hand.
>>
>> At last we can get rid of calculation and find early pgt related code.
>>
>> -v2: update to after fix_xen change,
>>      also use MACRO for initial pgt_buf size and add comments with it.
>> -v3: skip big reserved range in memblock.reserved near end.
>> -v4: don't need fix_xen change now.
>>
>> Suggested-by: "H. Peter Anvin" <hpa@...or.com>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>
> The changes to alloc_low_page and early_alloc_pgt_buf look OK to me.
>
> 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?
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