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

On 06/27/2012 07:59 PM, Minchan Kim wrote:

quoted

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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