[Linuxppc-users] memmap kernel option on ubuntu 16.04 power8

[Brian Horton]

On 09/27/2017 05:45 AM, Michael Ellerman wrote:
> Hi Brian,
> 
> Brian Horton <brianh at linux.vnet.ibm.com> writes:
>> Greetings all.
>>
>> I'm trying to run some tests with less memory than what's installed. the
>> 'mem=128G' option works, but it ends up putting all of the memory on the
>> first numa node:
> 
> It doesn't put memory anywhere, it just clamps the total memory, and it
> happens that the first (lowest address) 128G of RAM is all on node 0.

right, 'put' was a bad word choice. but yes, i see that the affect is 
that the first 128G of RAM is used.


> 
>> someone said that it worked on RHEL, so maybe it's an Ubuntu-specific bug..
> 
> OK that would be interesting, but I suspect it's not true :)

correct, on 2nd look it was mis-information. they confirmed that it 
doesn't work on RHEL either.

>> thoughts? ideas?
> 
> AFAIK there's no way to achieve what you're after, without changing
> kernel code or creating a custom device tree.
> 
> The mem= option is very primitive, it just clamps the total as I said
> above, it's not NUMA aware.
> 
> What hardware/platform are you trying to do this on? Are you familiar
> with kexec?

P8, Tuleta and Firestone, baremetal, ppc64le w/ Ubuntu 16.04 HWE kernel.

No, I haven't looked into anything with kexec - what are my options with 
that? I would prefer to stay away from building my own kernel code - 
i'll probably just live with the testing that i'm doing if that's my 
only option. i was just trying to be a little more 'realistic'.

Thanks!  .bri.


> cheers
>