[PATCH 0/4] Stop kswapd consuming 100% CPU when highest zone is small

[Mel Gorman <mgorman@suse.de>]

During allocator-intensive workloads, kswapd will be woken frequently
causing free memory to oscillate between the high and min watermark.
This is expected behaviour.  Unfortunately, if the highest zone is
small, a problem occurs.

This seems to happen most with recent sandybridge laptops but it's
probably a co-incidence as some of these laptops just happen to have
a small Normal zone. The reproduction case is almost always during
copying large files that kswapd pegs at 100% CPU until the file is
deleted or cache is dropped.

The problem is mostly down to sleeping_prematurely() keeping kswapd
awake when the highest zone is small and unreclaimable and compounded
by the fact we shrink slabs even when not shrinking zones causing a lot
of time to be spent in shrinkers and a lot of memory to be reclaimed.

Patch 1 corrects sleeping_prematurely to check the zones matching
	the classzone_idx instead of all zones.

Patch 2 avoids shrinking slab when we are not shrinking a zone.

Patch 3 notes that sleeping_prematurely is checking lower zones against
	a high classzone which is not what allocators or balance_pgdat()
	is doing leading to an artifical believe that kswapd should be
	still awake.

Patch 4 notes that when balance_pgdat() gives up on a high zone that the
	decision is not communicated to sleeping_prematurely()

This problem affects 3.0-rc4 and 2.6.38.8 for certain and is expected
to affect 2.6.39 as well. If accepted, they need to go to -stable to
be picked up by distros. This series is against 3.0-rc4. I've cc'd
people that reported similar problems recently to see if they still
suffer from the problem and if this fixes it.

 mm/vmscan.c |   57 ++++++++++++++++++++++++++++++++++-----------------------
 1 files changed, 34 insertions(+), 23 deletions(-)

-- 
1.7.3.4

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