Re: 9 TiB vm memory creation

[Ani Sinha]

On Tue, Feb 15, 2022 at 1:25 PM David Hildenbrand <david@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 <ani@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?

https://bugzilla-attachments.redhat.com/attachment.cgi?id=1795945