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

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Date:	Wed, 7 May 2008 18:39:48 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <andrea@...ranet.com>, 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:
> 
> > (That said, we're not running out of vm flags yet, and if we were, we 
> > could just add another word. We're already wasting that space right now on 
> > 64-bit by calling it "unsigned long").
> 
> We sure have enough flags.

Oh, btw, I was wrong - we wouldn't want to mark the vma's (they are 
unique), we need to mark the address spaces/anonvma's. So the flag would 
need to be in the "struct anon_vma" (and struct address_space), not in the 
vma itself. My bad. So the flag wouldn't be one of the VM_xyzzy flags, and 
would require adding a new field to "struct anon_vma()"

And related to that brain-fart of mine, that obviously also means that 
yes, the locking has to be stronger than "mm->mmap_sem" held for writing, 
so yeah, it would have be a separate global spinlock (or perhaps a 
blocking lock if you have some reason to protect anything else with this 
too).

			Linus
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