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

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Message-ID: <20121011144130.GB2408@localhost.localdomain>
Date:	Thu, 11 Oct 2012 10:41:32 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nel.org>
To:	Yinghai Lu <yinghai@...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 08:49:05AM -0700, Yinghai Lu wrote:
> 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),

What is T in here? Terabyte? Is the '[' vs ')' a significance in your
explanation? Should it be '[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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