On Mon, Aug 08, 2016 at 08:44:39AM +0300, Aldemir Akpinar wrote:
> > Sun, Aug 07, 2016 at 06:31:10PM +0200, Edward Bartolo wrote:
> >
> > On the other hand, full-machine virtualization costs you the max of
> > assigned
> > memory to that system, at all time.
>
> Going off-topic but I just wanted to correct this statement, when you're
> using full machine virtualization in the worst case it will use all the
> memory assigned to the server (unless you're using xen). Products like
> vmware or hyper-v uses in memory deduplication and swapping the virtual
> machine files to the disk to reduce the memory usage.

qemu-kvm (but not virtualbox) has support for KSM which, at a noticeable CPU
cost, deduplicates anonymous pages (on kvm all are anonymous) after a delay.
Both qemu-kvm and virtualbox can swap, too, but in that case you have double
swapping which means performance will be beyond terrible.

On the other hand, processes which mmap the same file will share the pages
at no cost or delay whatsoever. And under memory pressure, the system can
drop those frames without pointlessly swapping them to the disk.

--
An imaginary friend squared is a real enemy.