Re: KVM RAM limitation

[Brian Jackson <iggy@theiggy.com>]

On Wednesday 03 February 2010 02:06:53 pm Daniel Bareiro wrote:
> Hi, Anthony.
> 
> On Wednesday, 03 February 2010 13:20:12 -0600,
> 
> Anthony Liguori wrote:
> >>> Are you sure you enabled KVM? Are you sure you are using the KVM
> >>> binary and not some QEMU binary that's sitting around. This is one
> >>> of those situations where the KVM command you are running might
> >>> help.  Also the same binary you are running's version ($QEMU_BIN -h
> >>> 
> >>> | head -n1)
> >> 
> >> wilson:/usr/local/qemu-kvm/bin# ./qemu-system-x86_64 -h | head -n1
> >> QEMU PC emulator version 0.12.2 (qemu-kvm-0.12.2), Copyright (c)
> >> 2003-2008 Fabrice Bellard
> >> 
> >> 
> >> The procedure that I used to compile qemu-kvm is the same of always:
> >> to download qemu-kvm-0.12.2, to install the packages (Debian)
> >> zlib1g-dev and libpci-dev, and to compile of the following way:
> >> 
> >> # cd qemu-kvm-0.12.2
> >> # ./configure --prefix=/usr/local/qemu-kvm
> >> # make
> >> # make install
> >> 
> >> Until the moment I never got to use qemu-kvm with VMs of more than
> >> 2048 MB. In an installation that I have with KVM-88 and kernel x86_64
> >> I don't have this problem.
> > 
> > QEMU and KVM only support 2GB of memory on a 32-bit host.
> > 
> > Both need to create a userspace mapping of the guests memory.  In a
> > 32-bit environment, you only have enough usable address space in a
> > process to create a 2GB region.
> 
> But, according to what I read in the link [1] that commented, just by to
> have a x86_64 kernel would have to be sufficient to serve more than 2047
> MB of RAM.
> 

The kvm userspace would also have to be compiled as a 64bit binary. Possibly 
statically compiled somewhere else (if that's even possible) or with a 64bit 
chroot.



> Regards,
> Daniel
> 
> [1]
> https://help.ubuntu.com/community/KVM/Installation#Use%20a%2064%20bit%20ke
> rnel%20if%20possible