Kernel SRU request for changing kernel config submitted: https://lists.ubuntu.com/archives/kernel-team/2019-October/thread.html#104813 changing status to 'In Progress'
** Description changed: + 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. + __________ + The Ubuntu kernel configuration contains CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE=y for s390. This causes all standby memory configured for an LPAR to be used at IPL time. Note that this is definetaly not what a user wants on s390. The normal process is: define a certain amount of "base" memory which the system should use when IPL'ed, and define also a certain amount of "standby" memory which can be (also only partially) be additionaly used when necessary. Also note that it is *not* possible to add additional memory to a runnung system, besides the amount of memory specified as "standby". Therefore please change the kernel config option CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE to "n" for s390. ** Changed in: linux (Ubuntu) Status: New => In Progress ** Changed in: ubuntu-z-systems Status: Triaged => In Progress ** Changed in: ubuntu-z-systems Assignee: (unassigned) => Frank Heimes (frank-heimes) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1848492 Title: Change Config Option CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE for s390x from yes to no To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-z-systems/+bug/1848492/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs