linux-kernel - Re: [patch 00/19] VM pageout scalability improvements

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Date:	Fri, 04 Jan 2008 13:07:11 -0500
From:	Larry Woodman <lwoodman@...hat.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Eric Whitney <eric.whitney@...com>,
	Nick Dokos <nicholas.dokos@...com>
Subject: Re: [patch 00/19] VM pageout scalability improvements

Rik van Riel wrote:

>On Fri, 04 Jan 2008 17:34:00 +0100
>Andi Kleen <andi@...stfloor.org> wrote:
>  
>
>>Lee Schermerhorn <Lee.Schermerhorn@...com> writes:
>>
>>    
>>
>>>We can easily [he says, glibly] reproduce the hang on the anon_vma lock
>>>      
>>>
>>Is that a NUMA platform? On non x86? Perhaps you just need queued spinlocks?
>>    
>>
>
>I really think that the anon_vma and i_mmap_lock spinlock hangs are
>due to the lack of queued spinlocks.  Not because I have seen your
>system hang, but because I've seen one of Larry's test systems here
>hang in scary/amusing ways :)
>
Changing the anon_vma->lock into a rwlock_t helps because 
page_lock_anon_vma()
can take it for read and thats where the contention is.  However its the 
fact that under
some tests, most of the pages are in vmas queued to one anon_vma that 
causes so much
lock contention.


>
>With queued spinlocks the system should just slow down, not hang.
>
>  
>


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