** Changed in: linux (Ubuntu Bionic) Importance: Undecided => High -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. 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 -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
