> It seems the point of the balloon driver is to avoid forcing the host > to swap. For example, suppose I start a new guest OS. I check the > memory usage on the host and everything looks pretty good, maybe 30MB > used. Then suppose I run a recursive grep command in a Linux source > tree on the guest. The host memory usage will climb to the maximum > allotted memory as the guest OS fills its page cache with pages of > kernel source. Now, I go back to the host and decide I want to run > something a little memory intensive. The host has to swap and > dutifully copies those pages of kernel source to swap. Much better > would be if I could just chuck those pages and give them back to the > host, no swapping at all. > > Even if the guest has to swap, the reasoning is that the guest is in a > much better position to figure out what to swap than if the host were > forced to.
Worse, the guest might decide to swap out a page that's already swapped in by the host, forcing it to be read in again only to be immediately written out to disk by the guest :-( > It is a rather crude approach and I'm not sure how much practical > benefit there is, but I'll probably go ahead and code it up (at least > for a Linux host) if only for myself as it looks pretty simple. > (Linux 2.6.16 added the ability to punch holes in tmpfs files so all > the hard work should be done). I just wondered if there was anything > I was missing or if anyone had considered it before. Xen has a balloon driver - you might like to take a look at that for starters, and maybe borrow some code from it! There's been occasional talk to the effect that a number of projects might as well share functionality like ballooning since a number of systems require it. Cheers, Mark > > - E > > > _______________________________________________ > Qemu-devel mailing list > Qemu-devel@nongnu.org > http://lists.nongnu.org/mailman/listinfo/qemu-devel -- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
