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

[Calvin Sze]

Checked with BMC people, they said It cannot be done in BMC.


Calvin Sze
OpenSystem Enablement/Optimization
email: calvins at us.ibm.com




From:	"Jenifer Hopper" <jhopper at us.ibm.com>
To:	Brian Horton <brianh at linux.vnet.ibm.com>
Cc:	linuxppc-users at lists.ozlabs.org
Date:	09/27/2017 10:18 AM
Subject:	Re: [Linuxppc-users] memmap kernel option on ubuntu 16.04
            power8
Sent by:	"Linuxppc-users" <linuxppc-users-bounces
            +calvins=us.ibm.com at lists.ozlabs.org>



For FSP based systems you can go into the ASM and deconfigure dimms (System
Config -> HW Deconfig -> Mem Deconfig), but I don't know of a way to do
that for BMC based systems.

Thanks,
Jenifer Hopper
IBM Linux Technology Center, Linux Optimization
jhopper at us.ibm.com
(512) 286-6701

-----"Linuxppc-users" <linuxppc-users-bounces
+jhopper=us.ibm.com at lists.ozlabs.org> wrote: -----
To: Michael Ellerman <mpe at ellerman.id.au>, linuxppc-users at lists.ozlabs.org
From: Brian Horton
Sent by: "Linuxppc-users"
Date: 09/27/2017 10:12AM
Subject: Re: [Linuxppc-users] memmap kernel option on ubuntu 16.04 power8


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
>

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