[occi-wg] Extraction of requirements

[Chris Webb]

Richard Davies <richard.davies at elastichosts.com> writes:

> > and ulimit (for memory)?
> 
> Less interesting in this case, since the behaviour of the VM guest operating
> system is less linear. What should behaviour be if the operating system
> inside the VM believes it has 10GB of RAM, but the VM process has a ulimit
> of 2GB. What (should?) happen when the internal VM operating system
> allocates 2.1GB (as it believes it can!)?

In reality it's even worse than that. Something like kvm will just mmap an
area of address space corresponding to the physical address space it intends
to simulate. Consequently, if you ulimit the available virtual memory below
the level specified for the vm, it will fail to start altogether.

Perhaps one might think of a different mechanism from ulimit -v which
instead restricts the number of pages you're allowed to dirty, but what
should it do when a hypervisor process attempts to write to one page too
many? It's not a case of returning an error from a system call: you actually
have to refuse a write to memory that's already been malloced/mmaped, so
about all you could do is kill the process---probably not very friendly
behaviour to export to users!

Cheers,

Chris.