On Mon, 27 Jan 2020 08:39:25 +0100 Igor Mammedov <imamm...@redhat.com> wrote:
> On Fri, 24 Jan 2020 20:17:48 +0100 > Halil Pasic <pa...@linux.ibm.com> wrote: > > > On Thu, 23 Jan 2020 12:38:43 +0100 > > Igor Mammedov <imamm...@redhat.com> wrote: > > > > > With main RAM now converted to hostmem backends, there is no > > > point in keeping global mem_prealloc around, so alias > > > -mem-prealloc to "memory-backend.prealloc=on" > > > machine compat[*] property and make mem_prealloc a local > > > variable to only stir registration of compat property. > > > > > > *) currently user accessible -global works only with DEVICE > > > based objects and extra work is needed to make it work > > > with hostmem backends. But that is convenience option > > > and out of scope of this already huge refactoring. > > > Hence machine compat properties were used. > > > > AFAIU because of this something like > > -global memory-backend-file.share=on > > (as proposed by > > https://lists.nongnu.org/archive/html/qemu-devel/2019-12/msg00531.html) > > can not be used to make the main RAM shared (e.g. for vhost on s390x). > > Or am I wrong? If not, is -global still the way we want to make this work > > for non-numa machines, or did I miss updates? > > one should be able to use memory-backend property to make it work > instead of -m convenience option in s390 case. Thank you very much for the quick response! Honestly, I overlooked the memory-backed machine property, but regardless of that -machine,memory-backend=id *does not seem viable* at the moment. My understanding is that one has to do something like: -machine type=s390-ccw-virtio,memory-backend=mem \ -object memory-backend-file,id=mem,size=2G,mem-path=/dev/shm/virtiofs.shm,share=on \ I get qemu: : Device 'mem' not found because the 'memory-backend-*' objects are delayed, i.e. !object_create_initial(), and at the time when machine_set_property() tries to look the memory-backend up the memory-backend is not yet created. For why delayed, object_create_initial() has a comment: /* Memory allocation by backends needs to be done * after configure_accelerator() (due to the tcg_enabled() * checks at memory_region_init_*()). * * Also, allocation of large amounts of memory may delay * chardev initialization for too long, and trigger timeouts * on software that waits for a monitor socket to be created * (e.g. libvirt). */ if (g_str_has_prefix(type, "memory-backend-")) { Or, am I using it wrong? > > As for -global for objects (or more limited variant for memory-backends), > it needs more work to support objects. (that's mostly policy decision) > I agree. Regards, Halil