linux-kernel - Re: missing madvise functionality

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Date:	Wed, 4 Apr 2007 00:51:55 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	Eric Dumazet <dada1@...mosbay.com>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Jakub Jelinek <jakub@...hat.com>, linux-mm@...ck.org,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality

On Tue, Apr 03, 2007 at 02:46:09PM -0700, Ulrich Drepper wrote:
> Eric Dumazet wrote:
> > A page fault is not that expensive. But clearing N*PAGE_SIZE bytes is,
> > because it potentially evicts a large part of CPU cache.
> 
> *A* page fault is not that expensive.  The problem is that you get a
> page fault for every single page.  For 200k allocated you get 50 page
> faults.  It quickly adds up.

If you know in advance you need them it might be possible to 
batch that. e.g. MADV_WILLNEED could be extended to
work on anonymous memory and establish the mappings in the syscall. 
Would that be useful? 

-Andi
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