linux-kernel - Re: pud_bad vs pud

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Message-ID: <20090205234241.GA14203@elte.hu>
Date:	Fri, 6 Feb 2009 00:42:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Hugh Dickins <hugh@...itas.com>,
	William Lee Irwin III <wli@...ementarian.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: pud_bad vs pud_bad


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Ingo Molnar wrote:
>> We'd also lose a fair bit of performance (not to mention the pagetable  
>> footprint doubling that Hugh already mentioned) on 32-bit PAE capable  
>> systems that dont actually have RAM above 4G physical.
>
> Why's that?  Do you mean directly from using PAE, or as a side-effect of 
> highmem?

just the act of using PAE was measured to cause multi-percent slowdown in 
fork() and exec() latencies, etc. The pagetables are twice as large so is 
that really surprising?

	Ingo
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