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

-----Original Message----- From: Daniel P. Berrange [mailto:berrange@redhat.com] Sent: Monday, January 30, 2017 12:35 PM To: Michal Privoznik <mprivozn(a)redhat.com&gt; Cc: Safka, JaroslavX <jaroslavx.safka(a)intel.com>; libvir-list(a)redhat.com; Mooney, Sean K <sean.k.mooney(a)intel.com>; Ptacek, MichalX <michalx.ptacek(a)intel.com&gt; 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

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/ :|