[libvirt] [PATCHv4 0/3] Add support for file memorybacking

[Daniel P. Berrange]

On Sat, Jan 28, 2017 at 03:03:02PM +0100, Michal Privoznik wrote:
> On 13.12.2016 13:12, Jaroslav Safka wrote:
> > Hi,
> > we would like to introduce 3 new elements source,access and allocation in memoryBacking element.
> > For now it was made for numa topology.
> > 
> > <memoryBacking>
> >      <source type="file|anonymous"/>
> >      <access mode="shared|private"/>
> >      <allocation mode="immediate|ondemand"/>
> > </memoryBacking>
> > 
> > If allocation is immediate then -mem-prealloc should be added to the qemu commanline.
> > If source is file then
> > -object memory-backend-file,id=mem,size=1024M,mem-path=*lib dir path* -numa node,memdev=mem Will be added to the qemu commandline
> > 
> > If access is shared then the "share=on" parameter will be added to the memory-backend-file e.g.
> > -object memory-backend-file,id=mem,size=1024M,mem-path=/var/lib/libvirt/qemu,share=on
> > 
> > The access mode can be overriden by specifying token memAccess in numa cell.
> > 
> > The test cpu-numa-memshared was removed, because behaviour was changed and is not needed anymore
> 
> I beg to disagree. What if you don't have any <memoryBacking/>?
> 
> I like these patches, but I'm not certainly sure about:
> a) domain XML (in the past we used to require an ACK on schema change
> from one of the Dans)

What are you unsure about ?  This XML is what I suggested in previous
rounds of discussion.

> b) the location for qemu to create its mmaped files (patch 3/3).
> cfg->libDir looks very suspicious.

Well we've got two possibilities - source=anonymous, should be using
/dev/shm, similar to how we do huge pages. For source=file, we need
a real filesystem. Something under /var/lib/libvirt is reasonable.
Perhaps a dedicated dir is needed ? eg /var/lib/libvirt/ram in order
to provide a point where the admin can mount a sufficiently large
filesystem ? Or  make it configurable in /etc/libvirt/qemu.conf


Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://entangle-photo.org       -o-    http://search.cpan.org/~danberr/ :|