Re: [PATCH v3] mm: compaction: handle incorrect Unmovable type pageblocks

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On 04/26/2012 12:47 PM, Mel Gorman wrote:

Instead of COMPACT_ASYNC_PARTIAL and COMPACT_ASYNC_FULL should we have
COMPACT_ASYNC_MOVABLE and COMPACT_ASYNC_UNMOVABLE? The first pass from
the page allocator (COMPACT_ASYNC_MOVABLE) would only consider MOVABLE
blocks as migration targets. The second pass (COMPACT_ASYNC_UNMOVABLE)
would examine UNMOVABLE blocks, rescue them and use what blocks it
rescues as migration targets. The third pass (COMPACT_SYNC) would work
as it does currently. kswapd would only ever use COMPACT_ASYNC_MOVABLE.

That would avoid rescanning the movable blocks uselessly on the second
pass but should still work for Bartlomiej's workload.

What do you think?

This makes sense.

In other words, could it be better to always try to
rescue the unmovable blocks?

I do not think we should always scan within unmovable blocks on the
first pass. I strongly suspect it would lead to excessive amounts of CPU
time spent in mm/compaction.c.

Maybe my systems are not typical.  I have not seen
more than about 10% of the memory blocks marked as
unmovable in my system.

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