Subject: Re: page replacement
To: None <>
From: YAMAMOTO Takashi <>
List: tech-kern
Date: 12/10/2005 13:39:44

> > I agree that that change would keep pages around longer than the previous
> > mechanism for clearing the referenced bit.  does changing that back
> > make any detectable difference (either in measurable performance or
> > in a double-blind test of subjective performance)?
> i haven't done any serious comparison.

now i did a comparison.

- xen domainU with 40MB memory.
- page type balancing is disabled for simplicity.
- Y-axis is the number of major faults when linking a kernel.
  (ru_majflt, average of 3 runs.)
- X-axis is the percentage of inactive queue length.
  (the current value is 33%.)
- clrref=0 is the current behaviour.  clrref=1 means clearing
  the reference bit when moving pages from active queue to inactive queue.
- bln=N is the amount of memory in MB which is held by kernel to emulate
  low memory machine.  ("balloon size")

- same as the above, except Y-axis is elapsed time.

so i'd like to:
- put pmap_clear_reference back.  (clrref=1)
- make inactive queue length longer, or at least tunable.
  (i hesitate to to make it longer as it can have some negative impacts
  esp. for ports without h/w reference bits.)

any comments?