Re: [Xen-devel] [PATCH 5 of 8] Tools: Expose to libxc the total number of shared frames and space saved

[Adin Scannell <adin@xxxxxxxxxxxxxx>]

On Mon, Dec 12, 2011 at 10:43 PM, Andres Lagar-Cavilla
<andres@xxxxxxxxxxxxxxxx> wrote:
> used_frames indicates the number of frames of memory that are shared,
> each, by two or more domains. We use the term "frame" because it's
> commonly used in textbooks for MMUs, in the sense that "a frame hosts a
> page" or "a page maps to a frame". Thus our use of shared frames,
> representing a different page (albeit with identical contents) to
> different domains.

As Andres has pointed out, I named it frames to clearly differentiate
it from other page-based domctls (it worked!).  With the unusual
condition of multiple domains pointing to the same frame, the
nomenclature gets a bit hairy.  Any suggestions on this front?

> freed_pages indicates the number of individual pages freed as a result of
> sharing. These are pages, one per domain.

Here's a quick explanation and reason for these stats:

The way I see it, there are three easy-to-track, non-historical stats
about sharing.
X - The total number of domain pages that map to shared frames.
Y - The number of frames saved with sharing.
Z - The total number of shared frames (i.e. pages owned by dom_cow).

Any two of these will give you the third (via X = Y + Z).  In this
case, we used Y & Z because I think that they are the simplest to
reason about (and therefore the most likely to be wanted).  An
argument could easily be made for others though, if someone feels
strongly.

There are certainly some historical stats (# of unshares, etc.) and
lots of per-page/frame stats that would be of interest as well. But,
bit by bit...

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