Re: KVM RAM limitation

[Brian Jackson <iggy@theiggy.com>]

On Thursday 04 February 2010 11:47:13 am Daniel Bareiro wrote:
> Hi, Brian.
> 
> On Wednesday, 03 February 2010 16:44:28 -0600,
> 
> Brian Jackson wrote:
> > > 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.
> 
> Hmmm... and there is some way to compile qemu-kvm as a 64bit binary on a
> operating system userspace of 32bit?

I covered two options for doing that in my last email. You either build a 
static 64bit build on a 64bit host, or you install a 64bit chroot and 
compile/run from there.



> 
> I tried with ARCH=x86_64 with make but when using this I obtain several
> messages of the type "cast to/from pointer from/to integer of different
> size".
> 
> Thanks for your reply.
> 
> Regards,
> Daniel