Re: [PATCH] do_migrate_range: avoid failure as much as possible

[Wu Fengguang <fengguang.wu@intel.com>]

On Mon, Oct 25, 2010 at 11:09:01AM +0800, KAMEZAWA Hiroyuki wrote:
> On Mon, 25 Oct 2010 12:05:50 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
> > This changes behavior.
> > 
> > This "ret" can be > 0 because migrate_page()'s return code is
> > "Return: Number of pages not migrated or error code."
> > 
> > Then, 
> > ret < 0  ===> maybe ebusy
> > ret > 0  ===> some pages are not migrated. maybe PG_writeback or some
> > ret == 0 ===> ok, all condition green. try next chunk soon.
> > 
> > Then, I added "yield()" and --retrym_max for !ret cases.
>                                                ^^^^^^^^
> 						wrong.
> 
> The code here does
> 
> ret == 0 ==> ok, all condition green, try next chunk.

It seems reasonable to remove the drain operations for "ret == 0"
case.  That would help large NUMA boxes noticeably I guess.

> ret > 0  ==> all pages are isolated but some pages cannot be migrated. maybe under I/O
> 	     do yield.

Don't know how to deal with the possible "migration fail" pages --
sorry I have no idea about that situation at all.

Perhaps, OOM while offlining pages?

> ret < 0  ==> some pages may not be able to be isolated. reduce retrycount and yield()

Makes good sense.

Thanks,
Fengguang

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