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xen-devel
RE: [Xen-devel] [PATCH] linux/balloon: don't allow ballooningdowna domai
> > It might be the case though that, in practice, vm_committed_space is a
> > reasonable predictor for working set for some common types of workload. Many
> > applications probably keep their heaps fairly warm and hence in main memory.
Yes, and it also seems to be an "advance" predictor so that
the balloon driver has an opportunity to release pages to
a soon-to-be-memory-hungry domain before it really needs them
(or in case it might).
> I am dubious. What vm_committed_space does allow you to do
> however if you
> watch it in Xen is to actually ensure you never balloon out a virtual
> machine to the point you make it start killing stuff off.
Oddly, this is the opposite of what I observed. When I replaced
Jan's minimum_target calculation in the balloon driver with just
vm_committed_space (accidentally), I got lots of OOM's when I
was shutting down. So vm_committed_space CAN shrink too far
sometime and needs to be lower-bounded by some other calculated
minimum.
> There are better ways to measure memory pressure - sizes of the various
> active and inactive lists etc. OLPC has code for this and a proposed
> memory pressure notifier feature that they use to allow user space apps
> to cleanup.
Definitely agreed that vm_committed_space is just intended to be
a first order approximation. It also has the advantage of having
been around awhile so that the balloon driver will work with many
distros rather than require a TBD memory pressure indicator.
Alan, do you have a pointer to the proposed OLPC code?
Keir, I'm working on some xenbus support and will submit an
updated patch, probably early next week. I also have a horrible
hack to work in a module, but I suspect that will get jettisoned. ;-)
Thanks,
Dan
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