linux-kernel - Re: [PATCH 03/10] x86, mm: get early page table from BRK

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Date:	Wed, 10 Oct 2012 08:49:05 -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 03/10] x86, mm: get early page table from BRK

On Wed, Oct 10, 2012 at 7:17 AM, Konrad Rzeszutek Wilk
<konrad@...nel.org> wrote:
> On Tue, Oct 09, 2012 at 06:03:33PM -0700, Yinghai Lu wrote:

>> good point, i add one line comment to the revised patch.
>>
>> +/* need 3 4k for initial PMD_SIZE, 4k for 0-ISA_END_ADDRESS */
>
> Can you explain the math please? It sounds like this is based on
> the assumption that this you are using huge pages. But what if you
> are not? What if you can only do 4KB pages?

yes that is some extreme case:
assume that 2M range is [2T-2M, 2T),
one page for PGD-[2T-512g, 2T), one for PUD - [2T-1G, 2T), and one for
PMD -: [2T-2M, 2T)
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