APPLIED[Unstable]: [SRU][Bionic][Disco][Eoan][Patch 0/1] UBUNTU: [Config] Change Config Option CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE for s390x from yes to no

[Seth Forshee]

On Fri, Oct 18, 2019 at 09:05:20AM +0200, frank.heimes at canonical.com wrote:
> Buglink: https://bugs.launchpad.net/bugs/1848492
> 
> SRU Justification:
> 
> [Impact]
> 
> * By default all standby memory that is configured to an LPAR is used at boot (IPL) time.
> 
> * But the standby memory is meant to be added and used on demand later (after IPL).
> 
> [Fix]
> 
> * 0001-Ubuntu-Config-Disabled-CONFIG_MEMORY_HOTPLUG_DEFAULT.patch
> 
> [Test Case]
> 
> * Configure an LPAR in it's Activation Profile with a certain amount of 'Initial' memory and some 'Reserved' memory on top.
> 
> * Re-activate the LPAR to make the changes take effect and boot (IPL) Ubuntu.
> 
> * Check with the help of free whether the reported memory is only the initial memory (actual) or initial+reserved (desired).
> 
> [Regression Potential] 
> 
> * There is a certain regression potential, since some systems may have Initial and Reserved memory already defined today and have it already all in use under Linux (today obviously w/o having it dynamically added).
> 
> * If such a system got re-activated and rebooted, the memory size will then be what's defined as Initial memory and no longer Initial+Reserved.
> 
> * To be able to use the same size of the memory than before, the Reserved memory need to be either dynamically be added or the Initial memory re-configured to the sum of former Initial+Reserved.
> 
> * The latter case requires a re-activation of the LPAR, but since this corner case only happens after a reboot, a downtime is already in place for the re-activation.
> 
> * But overall the regression potential is low since it's for s390x only and the 'Reserved' memory option in the Activation Profile is rarely used.
> 
> [Other Info]
> 
> * In the past this config option was diabled for ppc64el, too.

Applied to unstable/master with context adjustments. Thanks!