Re: Using swap though there's plenty of mem free

[Przemyslaw Kacprzak <P.Kacprzak%elka.pw.edu.pl@localhost>]

Jonathan Schleifer wrote:
> Even after tweakig vm.filemax now:
>
> Memory: 171M Act, 90M Inact, 2120K Wired, 22M Exec, 23M File, 63M Free
> Swap: 257M Total, 63M Used, 194M Free
>
> 63 MB RAM unused. Not even for file cache. And still 63 MB swapped out?
> Why the hell that? I can understand that file cache is kept and instead
> pages swapped out, but in this case? There's really no reason for that
> kind of behaviour!
>   
As the others pointed out there is a reason for this kind of
behaviour (and i've this not only on NetBSD). When some
memory-intensive job starts up, other filecache is reduced, 
some thing are paged/swapped out. When this job is finished
these things are not swapped/paged in - the system doesn't which
of them will necessary in the near future (swapping/paging in
things that won't be accesed makes no sense they would need to
swapped out upon next memory request).

To reduce nuisance, you can try something like this:
-identify this memory intesive job (maybe it is some cron job), upon
finishing issue some request to your application so it get swapped in
- mlock/mlockall(2) (beware this may require more memory than
you think, also this memory-intensive jobs may really slow down)
- play with limits for this memory intensive jobs (I not sure if it
possible and how to do it).

Best Regards,
 Przemek Kacprzak