[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-users] detecting paging inside of VMs
The obvious way to do this would be to detect from inside
each domain that "I'm swapping a lot", and send a message (via networking most
obviously) to some monitor software within Dom0 that can take some suitable
action, rather than push this task into the less natural place of the
hypervisor. Since this is not something that needs millisecond resolution (or
you'd end up thrashing a lot), I think this is a workable solution. The hard
part of course is to determine what is "a lot" when it comes to swapping.
It should be possible to get this info without modifying
the kernel, just adding the suitable service software - which would be no
different from adding some other software to the guest to perform whatever task
it is supposed to perform.
For HVM it would be possible for the hypervisor to track
page-fault - I'm not sure if all page-faults are sent to Hypervisor for
Para-virtual guests (I don't know enough about para-virtual to answer that), but
the problem is that page-faults can happen for many different reasons, not just
swapping - pagefaults are for example used to indicate that a page has been
written to and need to be copied when using a "Copy on Write" variety of the
fork() system call - and if some system is doing a lot of fork calls, doesn't
mean that it needs more memory... So unless the hypervisor also understands the
REASON for a page-fault, it can't give any good indication of whether the guest
needs more memory...
--
Mats
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