Re: [PATCH] QEMU support for virtio balloon driver

[Dor Laor <dor.laor@gmail.com>]

On Mon, 2008-02-25 at 13:47 -0600, Anthony Liguori wrote:
> This patch adds support to QEMU for Rusty's recently introduce virtio balloon
> driver.  The user-facing portions of this are the introduction of a "balloon"
> and "info balloon" command in the monitor.
> 

The patch looks good. Might be a good idea to split it into 2 (balloon
vs s->vdev.get_config patch.

> Right now madvise() is commented out since it causes host panics.  Ballooning
> is still functional though--the host just doesn't reclaim the memory
> immediately.
> 

Since the mmu notifiers are not merged into 2.6.25 even, we need a
temporary solution for it.
There are two+ options:
1. Use the ksm (shared pages) scan and zero ballooned pages.
   This way the memory will be quickly picked up by the kernel.
2. Add in-kernel atomic ioctl for zapping the mmu + madvise
2+. Some sort of mmu notifiers backport (hard and hacky).

IMHO 2 is the best option.
btw: Izik's ksm module enable running 50 1G xp guests over a 16G host
even without the ballooning running!



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