Re: excessive CPU utilization by isolate_freepages?

[Minchan Kim <minchan@kernel.org>]

On 06/28/2012 09:28 AM, Rik van Riel wrote:

> On 06/27/2012 07:59 PM, Minchan Kim wrote:
> 
>> I doubt compaction try to migrate continuously although we have no
>> free memory.
>> Could you apply this patch and retest?
>>
>> https://lkml.org/lkml/2012/6/21/30
> 
> Another possibility is that compaction is succeeding every time,
> but since we always start scanning all the way at the beginning
> and end of each zone, we waste a lot of CPU time rescanning the
> same pages (that we just filled up with moved pages) to see if
> any are free.


It does make sense.

> 
> In short, due to the way compaction behaves right now,
> compaction + isolate_freepages are essentially quadratic.
> 
> What we need to do is remember where we left off after a
> successful compaction, so we can continue the search there
> at the next invocation.
> 


Good idea.
It could enhance parallel compaction, too.
Of course, if we can't meet the goal, we need loop around from start/end of zone.

-- 
Kind regards,
Minchan Kim

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