linux-kernel - Re: [PATCH 08 of 11] anon-vma-rwsem

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Message-ID: <alpine.LFD.1.10.0805071828110.3024@woody.linux-foundation.org>
Date:	Wed, 7 May 2008 18:32:11 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
cc:	Andrea Arcangeli <andrea@...ranet.com>,
	Andrew Morton <akpm@...ux-foundation.org>, steiner@....com,
	holt@....com, npiggin@...e.de, a.p.zijlstra@...llo.nl,
	kvm-devel@...ts.sourceforge.net, kanojsarcar@...oo.com,
	rdreier@...co.com, swise@...ngridcomputing.com,
	linux-kernel@...r.kernel.org, avi@...ranet.com, linux-mm@...ck.org,
	general@...ts.openfabrics.org, hugh@...itas.com,
	rusty@...tcorp.com.au, aliguori@...ibm.com, chrisw@...hat.com,
	marcelo@...ck.org, dada1@...mosbay.com, paulmck@...ibm.com
Subject: Re: [PATCH 08 of 11] anon-vma-rwsem



On Wed, 7 May 2008, Christoph Lameter wrote:
> On Wed, 7 May 2008, Linus Torvalds wrote:
> > and you're now done. You have your "mm_lock()" (which still needs to be 
> > renamed - it should be a "mmu_notifier_lock()" or something like that), 
> > but you don't need the insane sorting. At most you apparently need a way 
> > to recognize duplicates (so that you don't deadlock on yourself), which 
> > looks like a simple bit-per-vma.
> 
> Andrea's mm_lock could have wider impact. It is the first effective 
> way that I have seen of temporarily holding off reclaim from an address 
> space. It sure is a brute force approach.

Well, I don't think the naming necessarily has to be about notifiers, but 
it should be at least a *bit* more scary than "mm_lock()", to make it 
clear that it's pretty dang expensive. 

Even without the vmalloc and sorting, if it would be used by "normal" 
things it would still be very expensive for some cases - running thngs 
like ElectricFence, for example, will easily generate thousands and 
thousands of vma's in a process. 

		Linus
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