compiling a non-pae dom0 on a dell r710 with too much ram

compiling a non-pae dom0 on a dell r710 with too much ram

[Mike Sun]

Hi,

I've got a brand spankin new dell r710 with loads of memory on it,
except that I really want it to behave more like an older machine with
only 4G of RAM.  I've been trying to compile a dom0 without PAE for it
and can't seem to have much success.  I've constantly modified the
kernel config to turn off PAE and it either gets clobbered when I do a
make build-linux-2.6.18 or something.  Any ideas?

Mike

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Jeremy Fitzhardinge]

On 05/06/2010 04:00 PM, Mike Sun wrote:
> I've got a brand spankin new dell r710 with loads of memory on it,
> except that I really want it to behave more like an older machine with
> only 4G of RAM.  I've been trying to compile a dom0 without PAE for it
> and can't seem to have much success.  I've constantly modified the
> kernel config to turn off PAE and it either gets clobbered when I do a
> make build-linux-2.6.18 or something.  Any ideas?
>   

Xen doesn't support non-PAE 32 bit PV operation.  If you want to limit
memory, boot with dom0_mem=4G, and turn off HIGHMEM.

    J

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Mike Sun]

I'm working with Xen 3.2.2 so I believe it does support PAE 32-bit PV operation

On Thu, May 6, 2010 at 7:35 PM, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 05/06/2010 04:00 PM, Mike Sun wrote:
>> I've got a brand spankin new dell r710 with loads of memory on it,
>> except that I really want it to behave more like an older machine with
>> only 4G of RAM.  I've been trying to compile a dom0 without PAE for it
>> and can't seem to have much success.  I've constantly modified the
>> kernel config to turn off PAE and it either gets clobbered when I do a
>> make build-linux-2.6.18 or something.  Any ideas?
>>
>
> Xen doesn't support non-PAE 32 bit PV operation.  If you want to limit
> memory, boot with dom0_mem=4G, and turn off HIGHMEM.
>
>    J
>

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Jeremy Fitzhardinge]

On 05/06/2010 04:50 PM, Mike Sun wrote:
> I'm working with Xen 3.2.2 so I believe it does support PAE 32-bit PV operation
>   

Yes, it seems to have been dropped in 3.3.

Which kernel are you using?  I think all recent kernels have also
dropped support for non-PAE PV operation, so you would probably have to
go back to a kernel of that era to get non-PAE support.

But I'm not really sure what relevance PAE has to what you really want
to test.  Limited memory is a side-effect of non-PAE operation, but if
that's what you're concerned about you can easily limit memory size
(either by telling Xen to only use 4G of the system's memory, or by
limiting dom0 to 4G).

    J

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Mike Sun]

It's based off the 2.6.18.8 kernel.  Reason I can't have PAE is
because I had written some code a while back that touched shadow page
table stuff and I made changes assuming PAE wasn't being used.  I
don't think my code will work with PAE turned on.

On Thu, May 6, 2010 at 8:05 PM, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 05/06/2010 04:50 PM, Mike Sun wrote:
>> I'm working with Xen 3.2.2 so I believe it does support PAE 32-bit PV operation
>>
>
> Yes, it seems to have been dropped in 3.3.
>
> Which kernel are you using?  I think all recent kernels have also
> dropped support for non-PAE PV operation, so you would probably have to
> go back to a kernel of that era to get non-PAE support.
>
> But I'm not really sure what relevance PAE has to what you really want
> to test.  Limited memory is a side-effect of non-PAE operation, but if
> that's what you're concerned about you can easily limit memory size
> (either by telling Xen to only use 4G of the system's memory, or by
> limiting dom0 to 4G).
>
>    J
>

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Jeremy Fitzhardinge]

On 05/06/2010 05:09 PM, Mike Sun wrote:
> It's based off the 2.6.18.8 kernel.  Reason I can't have PAE is
> because I had written some code a while back that touched shadow page
> table stuff and I made changes assuming PAE wasn't being used.  I
> don't think my code will work with PAE turned on.
>   

Well that makes sense.  But are you running PV or HVM?   How does shadow
come into this?

    J

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Mike Sun]

it was for migration code that uses shadows in both PV and HVM mode.

On Thu, May 6, 2010 at 8:25 PM, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 05/06/2010 05:09 PM, Mike Sun wrote:
>> It's based off the 2.6.18.8 kernel.  Reason I can't have PAE is
>> because I had written some code a while back that touched shadow page
>> table stuff and I made changes assuming PAE wasn't being used.  I
>> don't think my code will work with PAE turned on.
>>
>
> Well that makes sense.  But are you running PV or HVM?   How does shadow
> come into this?
>
>    J
>

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Mike Sun]

> But I'm not really sure what relevance PAE has to what you really want
> to test.  Limited memory is a side-effect of non-PAE operation, but if
> that's what you're concerned about you can easily limit memory size
> (either by telling Xen to only use 4G of the system's memory, or by
> limiting dom0 to 4G).

How would tell Xen to only use 4G of the system's memory?

Re: compiling a non-pae dom0 on a dell r710 with too much ram

[Jeremy Fitzhardinge]

On 05/06/2010 05:51 PM, Mike Sun wrote:
>> But I'm not really sure what relevance PAE has to what you really want
>> to test.  Limited memory is a side-effect of non-PAE operation, but if
>> that's what you're concerned about you can easily limit memory size
>> (either by telling Xen to only use 4G of the system's memory, or by
>> limiting dom0 to 4G).
>>     
> How would tell Xen to only use 4G of the system's memory?
>   

Put "mem=4G" on its command line.

    J