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Date: Fri, 19 Jun 2009 23:19:34 +0200
From: Stefan Lankes <lankes@lfbs.rwth-aachen.de>
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To: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: "'Andi Kleen'" <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       linux-numa@vger.kernel.org, Boris Bierbaum <boris@lfbs.rwth-aachen.de>,
       "'Brice Goglin'" <Brice.Goglin@inria.fr>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [RFC PATCH 0/4]: affinity-on-next-touch
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Lee Schermerhorn wrote:
> On Thu, 2009-06-18 at 15:04 -0400, Lee Schermerhorn wrote:
>> On Thu, 2009-06-18 at 00:37 -0400, Lee Schermerhorn wrote:
>>> On Wed, 2009-06-17 at 09:45 +0200, Stefan Lankes wrote:
>>>>> I've placed the last rebased version in :
>>>>>
>>>>> http://free.linux.hp.com/~lts/Patches/PageMigration/2.6.28-rc4-mmotm-
>>>>> 081110/
>>>>>
>>>> OK! I will try to reconstruct the problem.
>>> Stefan:
>>>
>>> Today I rebased the migrate on fault patches to 2.6.30-mmotm-090612...
>>> [along with my shared policy series atop which they sit in my tree].
>>> Patches reside in:
>>>
>>> http://free.linux.hp.com/~lts/Patches/PageMigration/2.6.30-mmotm-090612-1220/
>>>
>> I have updated the migrate-on-fault tarball in the above location to fix
>> part of the problems I was seeing.  See below.
>>
>>> I did a quick test.  I'm afraid the patches have suffered some "bit rot"
>>> vis a vis mainline/mmotm over the past several months.  Two possibly
>>> related issues:
>>>
>>> 1) lazy migration doesn't seem to work. Looks like
>>> mbind(<some-policy>+MPOL_MF_MOVE+MPOL_MF_LAZY) is not unmapping the
>>> pages so, of course, migrate on fault won't work.  I suspect the
>>> reference count handling has changed since I last tried this.  [Note one
>>> of the patch conflicts was in the MPOL_MF_LAZY addition to the mbind
>>> flag definitions in mempolicy.h and I may have botched the resolution
>>> thereof.]
>>>
>>> 2) When the pages get freed on exit/unmap, they are still PageLocked()
>>> and free_pages_check()/bad_page() bugs out with bad page state.
>>>
>>> Note:  This is independent of memcg--i.e., happens whether or not memcg
>>> configured.
>>>
>> <snip>
>>
>> OK.  Found time to look at this.  Turns out I hadn't tested since
>> trylock_page() was introduced.  I did a one-for-one replacement of the
>> old API [TestSetPageLocked()], not noticing that the sense of the return
>> was inverted.  Thus, I was bailing out of the migrate_pages_unmap_only()
>> loop with the page locked, thinking someone else had locked it and would
>> take care of it.  Since the page wasn't unmapped from the page table[s],
>> of course it wouldn't migrate on fault--wouldn't even fault!
>>
>> Fixed this.
>>
>> Now:  lazy migration works w/ or w/o memcg configured, but NOT with the
>> swap resource controller configured.  I'll look at that as time permits.
> 
> Update:  I now can't reproduce the lazy migration failure with the swap
> resource controller configured.  Perhaps I had booted the wrong kernel
> for the test reported above.  Now the updated patch series mentioned
> above seems to be working with both memory and swap resource controllers
> configured for simple memtoy driven lazy migration.
> 

The current version of your patch works fine on my system. I tested the 
patches with our test applications and got very good performance results!

Stefan