KVM RAM limitation

KVM RAM limitation

[Daniel Bareiro]

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Hi all!

I'm trying to boot a VM with 2048 MB in a VMHost with Linux 2.6.32.6 and
qemu-kvm-0.12.2, but when doing it, I obtain it the following message:

qemu: at most 2047 MB RAM can be simulated.

This happened to me previously if in the VMHost I used kernel that is
not x86_64 [1], but it is not the case:

# uname -a
Linux wilson 2.6.32.6-dgb #1 SMP Mon Feb 1 17:10:30 ART 2010 x86_64 GNU/Linux


Which can be the problem?

Thanks in advance for your replies.

Regards,
Daniel

[1] https://help.ubuntu.com/community/KVM/Installation#Use%20a%2064%20bit%20kernel%20if%20possible
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Re: KVM RAM limitation

[Brian Jackson]

On Wednesday 03 February 2010 09:55:41 am Daniel Bareiro wrote:
> Hi all!
> 
> I'm trying to boot a VM with 2048 MB in a VMHost with Linux 2.6.32.6 and
> qemu-kvm-0.12.2, but when doing it, I obtain it the following message:
> 
> qemu: at most 2047 MB RAM can be simulated.

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)



> 
> This happened to me previously if in the VMHost I used kernel that is
> not x86_64 [1], but it is not the case:
> 
> # uname -a
> Linux wilson 2.6.32.6-dgb #1 SMP Mon Feb 1 17:10:30 ART 2010 x86_64
> GNU/Linux
> 
> 
> Which can be the problem?
> 
> Thanks in advance for your replies.
> 
> Regards,
> Daniel
> 
> [1]
> https://help.ubuntu.com/community/KVM/Installation#Use%20a%2064%20bit%20ke
> rnel%20if%20possible

Re: KVM RAM limitation

[Daniel Bareiro]

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On Wednesday, 03 February 2010 11:48:01 -0600,
Brian Jackson wrote:

> > I'm trying to boot a VM with 2048 MB in a VMHost with Linux 2.6.32.6
> > and qemu-kvm-0.12.2, but when doing it, I obtain it the following
> > message:
> > 
> > qemu: at most 2047 MB RAM can be simulated.

> 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.

Thanks for your reply.

Regards,
Daniel
-- 
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Re: KVM RAM limitation

[Anthony Liguori]

On 02/03/2010 01:08 PM, Daniel Bareiro wrote:
> On Wednesday, 03 February 2010 11:48:01 -0600,
> Brian Jackson wrote:
>
>    
>>> I'm trying to boot a VM with 2048 MB in a VMHost with Linux 2.6.32.6
>>> and qemu-kvm-0.12.2, but when doing it, I obtain it the following
>>> message:
>>>
>>> qemu: at most 2047 MB RAM can be simulated.
>>>        
>    
>> 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.

Regards,

Anthony Liguori

> Thanks for your reply.
>
> Regards,
> Daniel
>    

Re: KVM RAM limitation

[Daniel Bareiro]

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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.

Regards,
Daniel

[1] https://help.ubuntu.com/community/KVM/Installation#Use%20a%2064%20bit%20kernel%20if%20possible
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Re: KVM RAM limitation

[Brian Jackson]

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

Re: KVM RAM limitation

[Daniel Bareiro]

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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 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
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		-- D. E. Knuth

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Re: KVM RAM limitation

[Brian Jackson]

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