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

[Safka, JaroslavX]

> -----Original Message-----
> From: Daniel P. Berrange [mailto:berrange at redhat.com]
> Sent: Monday, January 30, 2017 12:35 PM
> To: Michal Privoznik <mprivozn at redhat.com>
> Cc: Safka, JaroslavX <jaroslavx.safka at intel.com>; libvir-list at redhat.com;
> Mooney, Sean K <sean.k.mooney at intel.com>; Ptacek, MichalX
> <michalx.ptacek at intel.com>
> Subject: Re: [libvirt] [PATCHv4 0/3] Add support for file memorybacking
> 
> 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
> 

[Jarek] It will be ok when I do something like libDir + "/ram". Or It should be configurable on compilation time?

> 
> Regards,
> Daniel
> --
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