Kernel SRU request submitted:
https://lists.ubuntu.com/archives/kernel-team/2019-November/thread.html#105478
Changing status in the 'Bionic' nomination to 'In Progress'
and status in 'linux (Ubuntu)' (which reflects the current development release,
hence today 'Focal' to 'Fix Released', since the patch got already upstream
accepted with 4.18.
** Changed in: linux (Ubuntu Bionic)
Status: New => In Progress
** Changed in: linux (Ubuntu)
Status: New => Fix Released
** Changed in: ubuntu-z-systems
Status: Confirmed => In Progress
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https://bugs.launchpad.net/bugs/1852257
Title:
s390/dasd: reduce the default queue depth and nr of hardware queues
Status in Ubuntu on IBM z Systems:
In Progress
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Bionic:
In Progress
Bug description:
SRU Justification:
==================
[Impact]
* On s390x systems with a small memory footprint, but large amounts of
DASD disks,
* the memory can get depleted (even during installation) which can
eventually lead to a situation where the OOM kicks in (followed by
even more problems).
* Starting with kernel 4.18 the patch below leads to 90% memory
consumption savings per active DASD device.
* The below backport is needed to fix this and get the improvement
into bionic's kernel 4.15.
[Fix]
* 3284da34a87ab7a527a593f89bbdaf6debe9e713 3284da3 "s390/dasd: reduce
the default queue depth and nr of hardware queues"
* Backport:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1852257/+attachment/5304830/+files/0001-s390
-dasd-reduce-the-default-queue-depth-and-nr-of-h.patch
[Test Case]
* Configure a s390x system (z/VM guest or LPAR) with only a bit RAM,
but lot's of DASDs devices.
* Now gradually enable more and more DASDs and monitor the memory
usage (be sure to exclude shared memory and cache).
* One can notice a difference in mem usage of about 10:1 per activated
DASD comparing the current stock 4.15 kernel with a patches kernel
4.15.
* With about less than 1GB memory and 40+ DASD devices one may start
to run into an OOM situation w(o the patch.
[Regression Potential]
* The regression potential can be considered as moderate, since:
* this is purely s390x specific
* it again only affects DASD disk storage (no zFCP/SCSI disk storage)
* and it's again only limited to smaller systems (so more z/VM guests
rather than LPARs).
[Other Info]
* A cherry-pick to 4.15 wasn't clean (problem in one line), hence the
backport, which applied, compiled and worked fine.
__________
This fix is already available with Ubuntu 18.10, but need also be
integrated into Ubuntu 18.04 LTS kernel (4.15).
This is available git-commit:
https://github.com/torvalds/linux/commit/3284da34a87a
Backport information will be provided.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu-z-systems/+bug/1852257/+subscriptions
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