Re: [Qemu-devel] [PATCH] augment info migrate with page status

[Glauber Costa <glommer@redhat.com>]

On Thu, May 21, 2009 at 03:05:04PM +0100, Daniel P. Berrange wrote:
> On Wed, May 20, 2009 at 07:20:05PM -0400, Glauber Costa wrote:
> > This patch augments info migrate output with status about:
> > * pages remaining
> > * pages transferred
> 
> Could you add 'pages total' and/or possibly 'page size', so apps 
> using this can more easily do calculations, without having to worry
> about hardcoding page sizes for each architecture they deal with. 
That can be done.

> 
> Oh, what happens if the guest is backed by huge pages ? Does the
> 'pages transferred' always count in terms of 4k pages, even if
> 2 M & 1 GB pages are in use ?
Right now, IIRC, migration code scan pages in multiples of TARGET_PAGE_SIZE.
we don't have any code path to deal with pages larger than that.

However, I believe it makes sense to be specific that we're talking about
TARGET_PAGE_SIZE pages. In the future, we may then have separate lines
for each kind of page being transferred.

In a nutshell, we can have something in the lines of:
pages total:
  X 4K pages
  Y 2M pages
pages remaining:
  X' 4k pages
  Y' 2M pages
pages transferred:
  X'' 4k pages
  Y'' 2M pages

Of course, 2M would only be shown in this example if we are really using any.

How do you feel about that?