linux-kernel - Re: [PATCH v2] X86-32: Allocate 256 bytes for pgd in PAE paging

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Date:	Thu, 18 Dec 2014 09:25:40 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Glenn Williamson <glenn.p.williamson@...el.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2] X86-32: Allocate 256 bytes for pgd in PAE paging

On 12/17/2014 01:47 PM, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> X86 32-bit machine and kernel use PAE paging, which currently wastes about
> 4K of memory per process on Linux where we have to reserve an entire page to
> support a single 256-byte PGD structure.  It would be a very good thing if
> we could eliminate that wastage.
> 

4*8 = 32 bytes, where did 256 bytes come from?

	-hpa


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