Re: [Xen-devel] question about xen4.4 features

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-05-22 at 10:40 +0100, George Dunlap wrote:
> >> 2.
> >> I tried the vm save feature by the command "xl save".
> >> And I found all the memory of the vm(my vm memory configuration is 4GB 
> >> )has been saved.
> >> The saved file size is almost 4GB.
> >> Whether it's right? Or any option I missed?
> >
> > No, this is normal and right.
> >
> >> Can I just save the valid content in the memory of the vm.
> >
> > If you balloon down only the non-ballooned pages will be stored. But
> > other than that the hypervisor doesn't know what memory is considered
> > valid by the guest OS.
> 
> Didn't Shriram implement an option to compress pages as they were sent
> over the wire?  One could imagine doing something similar for the save
> file (or indeed, zipping the entire file).  That would turn 0 pages
> into almost 0 bytes.

That did compression of subsequent rounds of live migration by only
sending the delta from the previous round, which doesn't help with a
normal save.

Someone was posting on xen-users@ about a hack to compress things:
http://lists.xen.org/archives/html/xen-users/2014-05/msg00073.html

I don't know how hard it would be to integrate properly into libxl/xl.
Might make an interesting project I suppose.

Ian.


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