Re: [Patch] memory unplug v3 [2/4] migration by kernel

[Mel Gorman <mel@csn.ul.ie>]

On Tue, 22 May 2007, Christoph Lameter wrote:

> On Tue, 22 May 2007, KAMEZAWA Hiroyuki wrote:
>
>> +config MIGRATION_BY_KERNEL
>> +	bool "Page migration by kernel's page scan"
>> +	def_bool y
>> +	depends on MIGRATION
>> +	help
>> +	  Allows page migration from kernel context. This means page migration
>> +	  can be done by codes other than sys_migrate() system call. Will add
>> +	  some additional check code in page migration.
>
> I think the scope of this is much bigger than you imagine. This is also
> going to be useful when Mel is going to implement defragmentation. So I
> think this should not be a separate option but be on by default.
>

I'm not 100% sure but chances are I need this.

I put together a memory compaction prototype today[*] to check because 
it's been put off long enough. However, memory compaction works whether I 
called migrate_pages() or migrate_pages_nocontext() even when regularly 
compacting under load. That said, calling migrate_pages() is probably 
racing like mad and I am not getting nailed for it as the test machine is 
small with one CPU and the stress load is kernel compiles instead of 
processes with mapped data. I'm basing compaction on top of a slightly 
modified version of this patch and will revisit it later.

Incidentally, the results of the compaction at rest are;

Freelists before compaction
Node    0, zone   Normal, type    Unmovable    302     55     26     20     12      6      2      0      0      0      0
Node    0, zone   Normal, type  Reclaimable   3165    734    218     28      3      0      0      0      0      0      0
Node    0, zone   Normal, type      Movable   4986   2222   1980   1553    752    238     26      2      0      0      0
Node    0, zone   Normal, type      Reserve      5      3      0      0      1      1      0      0      1      1      0

Freelists after compaction
Node    0, zone   Normal, type    Unmovable    278     32     14     12     10      5      4      2      0      0      0
Node    0, zone   Normal, type  Reclaimable   3184    743    226     32      3      0      0      0      0      0      0
Node    0, zone   Normal, type      Movable    862    676    599    421    238     94     17      6      4      3     31
Node    0, zone   Normal, type      Reserve      1      1      1      1      1      1      1      1      1      1      0

So it's doing something and the machine hasn't killed itself in the face. 
Aside, the page migration framework is ridiculously easy to work with - 
kudos to all who worked on it.

[*] Considering a working prototype only took a day to put
     together, I'm irritated it took me this long to get around to it.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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