Re: [Xen-devel] [PATCH v2 3/3] tools/libxc: use superpages during restore of HVM guest

[Olaf Hering <olaf@xxxxxxxxx>]

On Wed, Aug 23, Wei Liu wrote:

> On Tue, Aug 22, 2017 at 05:53:25PM +0200, Olaf Hering wrote:
> > In my testing I have seen the case of over-allocation. Thats why I
> > implemented the freeing of unpopulated parts. It would be nice to know
> > how many pages are actually coming. I think this info is not available.
> Not sure I follow. What do you mean by "how many pages are actually
> coming"?

This meant the expected number of pages to populate.

The value of p2m_size does not represent the actual number of pages
assigned to a domU. This info is stored in getdomaininfo.max_pages,
which is currently not used by restore. I will see if using this value
will avoid triggering the Over-allocation check.

> > On the other side, the first iteration sends the pfns linear. This is
> > when the allocation actually happens. So the over-allocation will only
> > trigger near the end, if a 1G range is allocated but only a few pages
> > will be stored into this range.
> This could be making too many assumptions on the data stream.

With the usage of max_pages some assumptions can be avoided.

Olaf

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