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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 23 May 2007 20:14:39 +0100 (IST)
Mel Gorman <mel@csn.ul.ie> wrote:

> 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.
> 
thank you for test :)

We (I and Goto-san) saw !page_mapped(page) case in try_to_unmap() under heavy
memory pressure,....swapping.
So, at least, 
==
+	if (page_mapped(page))
+		try_to_unmap(page, 1);
==
This change is necessary.

About anon_vma, see comments in page_remove_rmap().

> 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.
> 

I'll write this patch as one independent from memory unplug, AMAP.

Thanks,
-Kame

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