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Date: Fri, 6 Feb 2009 00:42:41 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Hugh Dickins <hugh@veritas.com>,
       William Lee Irwin III <wli@movementarian.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: pud_bad vs pud_bad
Message-ID: <20090205234241.GA14203@elte.hu>
References: <498B2EBC.60700@goop.org> <20090205184355.GF5661@elte.hu> <498B35F9.601@goop.org> <20090205191017.GF20470@elte.hu> <Pine.LNX.4.64.0902051921150.30938@blonde.anvils> <498B4F1F.5070306@goop.org> <Pine.LNX.4.64.0902052046240.18431@blonde.anvils> <498B54A0.7040005@goop.org> <20090205215050.GB28097@elte.hu> <498B6325.1040401@goop.org>
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* Jeremy Fitzhardinge <jeremy@goop.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