Hi,

Another attempt.

With this patch I get noticeable improvements in streaming write +16%!
(streaming write throughput is close to streaming read :-)

dbench results are mixed - slightly worse than plain test5-1...
It now survives mmap002, as opposed to vmfix-2.x :-)  there were
bugs of cause.

* Basic idea in this patch is to keep free pages of zones in the
  range [pages_high ... pages_low]. Kswapd will only run until
  one zone gets pages_high. In this situation pages from all zones
  are free able.
* In addition kswapd will run if any zone has less than pages_low.

* Actually implemented by using three values in zone_wake_kswapd
  0 = zone initially above pages_high, allocs allowed until zone
      gets < pages_low
  1 = zone < pages_low
 -1 = additional alloc done after zone become < pages_low
 Most of the time there will only be one zone to with
 zone_wake_kswapd zero. This zone will get the allocs until it
 also gets < pages_low, then kswapd starts and runs until any
 zone gets > pages_high - it will probably be another zone. Now
 that one gets the allocs, ...

* There are some additional stuff that needs cleaning / further
  investigations.


/RogerL

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