linux-kernel - Re: [RFC][PATCH 6/8] mm: handle_speculative

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Date:	Thu, 07 Jan 2010 18:51:36 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	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 01/07/2010 12:36 PM, Linus Torvalds wrote:
> On Thu, 7 Jan 2010, Peter Zijlstra wrote:
>>
>> Right, supposing we can make this speculative fault stuff work, then we
>> can basically reduce the mmap_sem usage in fault to:
>>
>>    - allocating new page tables
>>    - extending the growable vmas
>>
>> And do everything else without holding it, including zeroing and IO.
>
> Well, I have yet to hear a realistic scenario of _how_ to do it all
> speculatively in the first place, at least not without horribly subtle
> complexity issues. So I'd really rather see how far we can possibly get by
> just improving mmap_sem.

I would like to second this sentiment.  I am trying to make the
anon_vma and rmap bits more scalable for multi-process server
workloads and it is quite worrying how complex locking already
is.

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