On Wed, 27 Jun 2012, Rik van Riel 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

Not sure if Jim is using memcg; if not, then this won't be helpful.

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.

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.

So when the free and migration scanners meet and compact_finished() == 
COMPACT_CONTINUE, loop around to the start of the zone and continue until 
you reach the pfn that it was started at?  Seems appropriate.

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