On 12/06/2017 01:04 PM, David Hildenbrand wrote: > On 06.12.2017 13:00, Christian Borntraeger wrote: >> KVM does not allow memory regions > KVM_MEM_MAX_NR_PAGES, basically >> limiting the memory per slot to 7.999TB. Lets split the base memory >> into 4TB chunks to allow go beyond 8TB for a guest. With that (and >> optimistic overcommitment in the kernel) I was able to start a 59TB >> guest on a 1TB system. >> >> Signed-off-by: Christian Borntraeger <[email protected]> >> --- >> hw/s390x/s390-virtio-ccw.c | 20 +++++++++++++++++--- >> 1 file changed, 17 insertions(+), 3 deletions(-) >> >> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c >> index 8425534..6735bbb 100644 >> --- a/hw/s390x/s390-virtio-ccw.c >> +++ b/hw/s390x/s390-virtio-ccw.c >> @@ -157,11 +157,25 @@ static void virtio_ccw_register_hcalls(void) >> static void s390_memory_init(ram_addr_t mem_size) >> { >> MemoryRegion *sysmem = get_system_memory(); >> - MemoryRegion *ram = g_new(MemoryRegion, 1); >> + ram_addr_t chunk, offset; >> + gchar *name; >> >> /* allocate RAM for core */ >> - memory_region_allocate_system_memory(ram, NULL, "s390.ram", mem_size); >> - memory_region_add_subregion(sysmem, 0, ram); >> + offset = 0; >> + while (mem_size) { >> + MemoryRegion *ram = g_new(MemoryRegion, 1); >> + chunk = mem_size; >> + /* KVM does not allow memslots >= 8 TB. Lets split into 4TB chunks >> */> + if (chunk > 4UL * 1024 * 1024 * 1024 * 1024) { >> + chunk = 4UL * 1024 * 1024 * 1024 * 1024; >> + } >> + name = g_strdup_printf("s390.ram[0x%lx]", offset); >> + memory_region_allocate_system_memory(ram, NULL, name, chunk); >> + memory_region_add_subregion(sysmem, offset, ram); >> + mem_size -= chunk; >> + offset += chunk; >> + g_free(name); >> + } >> >> /* Initialize storage key device */ >> s390_skeys_init(); >> > > This will most certainly break migration, no?
Probably yes. Thats why the patch has RFC. I was looking for ideas. > > 1. I remember the name being used for migration, I might be wrong. > 2. Migration of guests > 4TB is certainly broken ;) > > I wonder if this should rather be handled in the kvm_slot code. > (silently create an manage two slots)
