Xen devel - May 2010 - compiling a non-pae dom0 on a dell r710 with too much ram

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

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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

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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
>
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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

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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
>
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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

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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
>
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> 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?

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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

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