Re: [PATCH 1/5] qemu.conf changes to support multiple memory backend directories

Hi Martin, Answers inline. Thanks for helping with the review and all the tips! On 3/1/24 04:00, Martin Kletzander wrote: > On Mon, Jan 29, 2024 at 04:43:53PM -0500, mgalaxy(a)akamai.com wrote: >> From: Michael Galaxy <mgalaxy(a)akamai.com&gt; >> > >> In our case, we almost always have two NUMA nodes, so in that >> example, we have two PMEM regions which are created on the >> Linux kernel command line that get mounted into those two >> locations for libvirt to use. >> > > There are PMEM devices which you then expose as filesystems to use for > libvirt as a backing for VM's PMEMs.  Do I understand that correctly? > > If yes, how are these different?  Can't they be passed through? > So, these are very different. QEMU currently already supports passing through PMEM for guest internal use (The guest puts its own filesystem onto the passed-through PMEM device). In our case, we are using the PMEM area only in the host to place the QEMU memory backing for all guests into a single PMEM area. To support NUMA correctly, QEMU needs to support mutiple host-level PMEM areas which have been pre-configured to be NUMA aware. This is strictly for the

purposes of doing live updates, not as a mechanism for guests to internally take advantage of persistent memory... that's a completely different use case (which in and of itself is very interesting, but not what we are using it for). That's how it works. Does that make sense? (I'll work on those other requests, thank you) - Michael