On 15.02.22 10:40, Ani Sinha wrote: > On Tue, Feb 15, 2022 at 2:08 PM David Hildenbrand <da...@redhat.com> wrote: >> >> On 15.02.22 09:12, Ani Sinha wrote: >>> On Tue, Feb 15, 2022 at 1:25 PM David Hildenbrand <da...@redhat.com> wrote: >>>> >>>> On 15.02.22 08:00, Ani Sinha wrote: >>>>> >>>>> >>>>> On Mon, 14 Feb 2022, David Hildenbrand wrote: >>>>> >>>>>> On 14.02.22 13:36, Igor Mammedov wrote: >>>>>>> On Mon, 14 Feb 2022 10:54:22 +0530 (IST) >>>>>>> Ani Sinha <a...@anisinha.ca> wrote: >>>>>>> >>>>>>>> Hi Igor: >>>>>>>> >>>>>>>> I failed to spawn a 9 Tib VM. The max I could do was a 2 TiB vm on my >>>>>>>> system with the following commandline before either the system >>>>>>>> destabilized or the OOM killed killed qemu >>>>>>>> >>>>>>>> -m 2T,maxmem=9T,slots=1 \ >>>>>>>> -object >>>>>>>> memory-backend-file,id=mem0,size=2T,mem-path=/data/temp/memfile,prealloc=off >>>>>>>> \ >>>>>>>> -machine memory-backend=mem0 \ >>>>>>>> -chardev file,path=/tmp/debugcon2.txt,id=debugcon \ >>>>>>>> -device isa-debugcon,iobase=0x402,chardev=debugcon \ >>>>>>>> >>>>>>>> I have attached the debugcon output from 2 TiB vm. >>>>>>>> Is there any other commandline parameters or options I should try? >>>>>>>> >>>>>>>> thanks >>>>>>>> ani >>>>>>> >>>>>>> $ truncate -s 9T 9tb_sparse_disk.img >>>>>>> $ qemu-system-x86_64 -m 9T \ >>>>>>> -object >>>>>>> memory-backend-file,id=mem0,size=9T,mem-path=9tb_sparse_disk.img,prealloc=off,share=on >>>>>>> \ >>>>>>> -machine memory-backend=mem0 >>>>>>> >>>>>>> works for me till GRUB menu, with sufficient guest kernel >>>>>>> persuasion (i.e. CLI limit ram size to something reasonable) you can >>>>>>> boot linux >>>>>>> guest on it and inspect SMBIOS tables comfortably. >>>>>>> >>>>>>> >>>>>>> With KVM enabled it bails out with: >>>>>>> qemu-system-x86_64: kvm_set_user_memory_region: >>>>>>> KVM_SET_USER_MEMORY_REGION failed, slot=1, start=0x100000000, >>>>>>> size=0x8ff40000000: Invalid argument >>>>>>> >>>>> >>>>> I have seen this in my system but not always. Maybe I should have dug >>>>> deeper as to why i do see this all the time. >>>>> >>>>>>> all of that on a host with 32G of RAM/no swap. >>>>>>> >>>>> >>>>> My system in 16 Gib of main memory, no swap. >>>>> >>>>>> >>>>>> #define KVM_MEM_MAX_NR_PAGES ((1UL << 31) - 1) >>>>>> >>>>>> ~8 TiB (7,999999) >>>>> >>>>> That's not 8 Tib, thats 2 GiB. But yes, 0x8ff40000000 is certainly greater >>>>> than 2 Gib * 4K (assuming 4K size pages). >>>> >>>> "pages" don't carry the unit "GiB/TiB", so I was talking about the >>>> actual size with 4k pages (your setup, I assume) >>> >>> yes I got that after reading your email again. >>> The interesting question now is how is redhat QE running 9 TiB vm with kvm? >> >> As already indicated by me regarding s390x only having single large NUMA >> nodes, x86 is usually using multiple NUMA nodes with such large memory. >> And QE seems to be using virtual numa nodes: >> >> Each of the 32 virtual numa nodes receive a: >> >> -object memory-backend-ram,id=ram-node20,size=309237645312,host- >> nodes=0-31,policy=bind >> >> which results in a dedicated KVM memslot (just like each DIMM would) >> >> >> 32 * 309237645312 == 9 TiB :) > > ah, I should have looked closely at the other commandlines before > shooting off the email. Yes the limitation is per mem-slot and they > have 32 slots one per node. > ok so should we do > kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES); > from i386 kvm_arch_init()?
As I said, I'm not a friend of these workarounds in user space. Assume you have one KVM memslot left and you hotplug a huge DIMM that will consume more than one KVM memslot -- you're in trouble, because hotplug will succeed but creating the second memslot will fail. So you need additional logic in memory device code to special-case on these corner cases. We should try increasing the limit in KVM and handle it gracefully in QEMU. But that's just my 2 cents. -- Thanks, David / dhildenb
