Re: [Qemu-devel] [PATCH v4 08/11] dump-guest-memory: add qmp event DUMP_COMPLETED

[Peter Xu <peterx@redhat.com>]

On Wed, Dec 02, 2015 at 09:01:16AM -0700, Eric Blake wrote:
> On 12/02/2015 08:21 AM, Peter Xu wrote:
> > Will the raw memory total size useful in any way? I am totally ok to
> > add this, just failed to find a way for user to use it besides
> > calculating finished work during dump... :(
> 
> Good idea.  You never know if it will be helpful, but the information is
> basically free to provide and doesn't seem like too much of a
> maintenance burden to promise to always include the total.  And in the
> case of an error, knowing the final values of complete/total might also
> be useful to see how far things got before failure (for example, if it
> failed because of ENOSPACE, knowing how much was complete may give an
> idea of how much additional space should be added before retrying).

Yes, it's more meaningful when it fails. And maybe you are right,
it's free to provide it. :)

I can add it in v5.

One thing to mention is that, since the written_byte field is only
for raw memory size, which means (e.g., for kdump-zlib), the number
could first goes to 70% of total very quickly in less than a second
(possibly due to zero pages, so actually very little data is written
to disk), then it will use another ten seconds to finish the rest
30% (which contains most of the data of the final dump file). So the
number would still help little even with ENOSPACE. When user sees a
70% of "written" when failed, it will not mean "we need extra of 30%
more spaces", it actually means "we need 100% more", but the user
would never figure out the real situation from the number only. :(

Thanks!
Peter

> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>