Re: How to limit amount of virtual memory used for files (was: Re: Tuning ZFS memory usage on NetBSD - call for advice)

[mlelstv%serpens.de@localhost (Michael van Elst)]

lloyd%must-have-coffee.gen.nz@localhost (Lloyd Parkes) writes:

>HÃ¥vard's email about his G4 Mac Mini is an excellent example 
>of a problem. A problem I have experienced in the past was a program 
>failing with out of memory errors while processing 128MB of data on a 
>system with 256MB of RAM. A problem doesn't have to be a crash. It could 
>simply be unnecessary swap being used leading to terrible performance.

Swapping might be cheaper than trashing the file cache, it all depends
on your particular workload.

I don't think there is a smart heuristic that covers all (or just most)
cases. Even the current default tuning values used to be good (and are
probably still mostly good for a G4 Mac Mini).


There is a second issue, that occurs more frequently and is independent
of the VM tuning.

The system will buffer all output until it runs out of memory (short
of hitting secondary limits like the pager map on some systems).
We don't reserve enough memory nor react in a smart way to handle
this situation, and we don't put any pressure on applications
wasting memory that way.