SysIII swapping strangeness
John Kullmann
jk at plx.UUCP
Fri Aug 9 11:14:45 AEST 1985
The stock swap algorithm will swap out a process which
has been in memory for 2 seconds (regardless of whether it
got *any* cpu time or not since it was swapped in) and swap
in a selected swapped out process that has been out for
at least 2 seconds.
Consider a heavily memory (over)loaded system, sometimes
swapping continuously for 5-20 minutes at a time. Is it
possible that processes are being swapped in and back out
many many times before they actually run? (some of these
processes are > 500Kb).
A few questions:
1) Is this 2 second business left over from the pdp11
where the address spaces were smaller? Should
I/do people change this?
2) Shouldn't the swapper be changed to at least let the
poor sucker get a few ticks before letting him
go back out?
3) Do all un*x systems (before demand paging came around)
slow way,way,way down when anything but trivial
swapping is occurring?
4) Has anyone else researched this? If so, please save me
some time and respond...
John Kullmann
...decvax!sun!plx!jk
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