Re: [PATCH v2] qemu: Don't prealloc mem for real NVDIMMs

Currently, we configure QEMU to prealloc memory almost by default. Well, by default for NVDIMMs, hugepages and if user asked us to (via memoryBacking <allocation mode="immediate"/>). However, when guest's NVDIMM is backed by real life NVDIMM this approach is not the best. In this case users should put <pmem/> into the <memory/> device <source/>, like this: <memory model='nvdimm' access='shared'> <source> <path>/dev/pmem0</path> <pmem/> </source> </memory> Instructing QEMU to do prealloc in this case means that each page of the NVDIMM is "touched" (the first byte is read and written back - see QEMU commit v2.9.0-rc1~26^2) which cripples device wear. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1894053 Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- v2 of: https://www.redhat.com/archives/libvir-list/2020-November/msg01568.html diff to v1: - I've dropped the first hunk of v1 which forbade prealloc even if user requested it explicitly. src/qemu/qemu_command.c | 5 ++++- .../memory-hotplug-nvdimm-pmem.x86_64-latest.args | 2 +- 2 files changed, 5 insertions(+), 2 deletions(-)