linux-kernel - Re: [PATCH 12/19] x86, mm: Add alloc_low

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Message-ID: <CAE9FiQUcTQ_7ztmLS=z20j4m6KqJKQXX58UHL7AUHn8XHdTa8w@mail.gmail.com>
Date:	Mon, 22 Oct 2012 12:24:41 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Konrad Rzeszutek Wilk <konrad@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, Jacob Shin <jacob.shin@....com>,
	Tejun Heo <tj@...nel.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/19] x86, mm: Add alloc_low_pages(num)

On Mon, Oct 22, 2012 at 8:17 AM, Konrad Rzeszutek Wilk
<konrad@...nel.org> wrote:
> On Thu, Oct 18, 2012 at 01:50:23PM -0700, Yinghai Lu wrote:
>> 32bit kmap mapping need page table to be used for low to high.
>                                     ^-s
>
>>
>> At this point those page table are still from pgt_buf_* from BRK,
>                                 ^s
>
>> So it is ok now.
>> But we want to move early_ioremap_page_table_range_init() out of
>> init_memory_mapping() and only call it one time later, that will
>> make page_table_range_init/page_table_kmap_check/alloc_low_page to
>> use memblock to get page.
>>
>> memblock allocation for page table are from high to low.
>                                     ^s
>>
>> So will get panic from page_table_kmap_check() that has BUG_ON to do
>> ordering checking.
>>
>> This patch add alloc_low_pages to make it possible to alloc serveral pages
>> at first, and hand out pages one by one from low to high.
>
> .. But for right now this patch just makes it by default one.

?

---
32bit kmap mapping needs pages to be used for low to high.

At this point those pages are still from pgt_buf_* from BRK, so it is
ok now.
But we want to move early_ioremap_page_table_range_init() out of
init_memory_mapping() and only call it one time later, that will
make page_table_range_init/page_table_kmap_check/alloc_low_page to
use memblock to get page.

memblock allocation for pages are from high to low.

So will get panic from page_table_kmap_check() that has BUG_ON to do
ordering checking.

This patch add alloc_low_pages to make it possible to alloc serveral pages
at first, and hand out pages one by one from low to high.

-v2: add one line comment about xen requirements.
---
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