linux-kernel - Re: missing madvise functionality

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Date:	Wed, 04 Apr 2007 20:05:54 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jakub Jelinek <jakub@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality

Eric Dumazet wrote:

> Well, I believe this one is too expensive. I was thinking of a light one :

This one seems worse. Passing your vm_area_cache around everywhere, which
is just intrusive and dangerous because ot becomes decoupled from the mm
struct you are passing around. Watch this:


> @@ -1638,7 +1652,7 @@ find_extend_vma(struct mm_struct * mm, u
>  	unsigned long start;
>  
>  	addr &= PAGE_MASK;
> -	vma = find_vma(mm,addr);
> +	vma = find_vma(mm,addr,&current->vmacache);
>  	if (!vma)
>  		return NULL;
>  	if (vma->vm_start <= addr)

So now you can have current calling find_extend_vma on someone else's mm
but using their cache. So you're going to return current's vma, or current
is going to get one of mm's vmas in its cache :P

-- 
SUSE Labs, Novell Inc.
-
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