On Wed, 11 Nov 2009 10:37:56 am Anthony Liguori wrote: > Rusty Russell wrote: > > You register an outbuf at initialization time. The host hands it back when > > it wants you to refill it with stats. > > That's strangely backwards. Guest send a stat buffer that's filled out, > host acks it when it wants another. That doesn't seem bizarre to you?
Yep! But that's a limitation of our brains, not the infrastructure ;) Think of the stats as an infinite stream of data. Read from it at your leisure. This is how, for example, console output works. > > But the universe is remarkably indifferent to what we want. Is it actually > > sufficient or are we going to regret our laziness? > > It's not laziness, it's consistency. How is actual different than free > memory or any other stat? Because it's a COLLECTION of stats. For example, swap in should be < swap out. Now, the current Linux implementation of all_vm_events() is non-atomic anyway, so maybe we can just document this as best-effort. I'm saying that if it *is* a problem, I think we need a vq. But it raises the question: what stats are generally useful cross-OS? Should we be supplying numbers like "unused" (free) "instantly discardable" (ie. clean), "discardable to disk" (ie. file-backed), "discardable to swap" (ie. swap-backed) and "unswappable" instead? (I just made those up, of course, but it seems like that would give a fair indication of real memory pressure in any OS). Thanks, Rusty.
