Re: [9fans] Kernel panic when allocating a huge memory

[erik quanstrom <quanstro@quanstro.net>]

>
> This makes more sense.  However, if your hypervisor is swapping, you've
> screwed up your planning.  RAM oversubscription is the reason most
> dime-store VPS services suck really badly.  I leave swapping to the
> guest OS, since that's where malloc is being called.

i'm not a big vm guy, but i do know that oversubscription is a big problem.

however, i think that queuing theory in general says that one queue with global
sorting beats n smaller queues with local sorting.  i think this is sometimes called the
checkout-line problem.

other factors, like global knowledge of memory use stats and page duplication
should put the vm in an even better position than general queueing theory
would suggest to make decisions on what pages to move to disk wrt. global
(that is total machine) throughput.

do you have a reference that demonstrates or derives that a similarly-loaded
machine can perform better with all the guests swapping indepdently and
the vm not swapping, rather than preventing the guests from swapping and
letting the vm swap?

- erik