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

[frank.heimes at canonical.com]

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.

Frank Heimes (1):
  Ubuntu: [Config] Disabled CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE on
    s390x

 debian.master/config/annotations               | 4 ++--
 debian.master/config/s390x/config.common.s390x | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

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2.7.4