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Message-ID: <1262900683.4049.139.camel@laptop>
Date: Thu, 07 Jan 2010 22:44:43 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christoph Lameter <cl@...ux-foundation.org>,
Arjan van de Ven <arjan@...radead.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"minchan.kim@...il.com" <minchan.kim@...il.com>,
"hugh.dickins" <hugh.dickins@...cali.co.uk>,
Nick Piggin <nickpiggin@...oo.com.au>,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()
On Thu, 2010-01-07 at 10:44 -0800, Linus Torvalds wrote:
>
> On Thu, 7 Jan 2010, Linus Torvalds wrote:
> >
> > For example: there's no real reason why we take mmap_sem for writing when
> > extending an existing vma. And while 'brk()' is a very oldfashioned way of
> > doing memory management, it's still quite common. So rather than looking
> > at subtle lockless algorithms, why not look at doing the common cases of
> > an extending brk? Make that one take the mmap_sem for _reading_, and then
> > do the extending of the brk area with a simple cmpxchg or something?
>
> I didn't use cmpxchg, because we actually want to update both
> 'current->brk' _and_ the vma->vm_end atomically, so here's a totally
> untested patch that uses the page_table_lock spinlock for it instead (it
> could be a new spinlock, not worth it).
>
> It's also totally untested and might be horribly broken. But you get the
> idea.
>
> We could probably do things like this in regular mmap() too for the
> "extend a mmap" case. brk() is just especially simple.
I haven't yet looked at the patch, but isn't expand_stack() kinda like
what you want? That serializes using anon_vma_lock().
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