Yes, this is memory fragmentation. Heiko recently did some changes that should improve the situation.
This upstream change https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=cd4386a931b6310b05559d2e28efda04d30ab593 will change the allocation from below 2GB to whereever is enough space left which should improve the situation for larger guests. We will try to integrate that into existing distro as a backport. Long term we try to solve the issue in a more generic way: Newer kernel contain a feature called contiguous memory allocator and the upstream commit https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=3f4298427ad521fdc74fb991b17d84959513218a does use this allocator for vmcp. The downside is, that this will be harder/impossible to backport as older kernels miss the CMA infrastructure. Christian On 10/18/2017 07:50 PM, Neale Ferguson wrote: > Fragmentation. Vmcp needs contiguous real storage. So if there is not a > slab of 1MB in size hanging around then it will complain. > > On 10/18/17, 1:44 PM, "Linux on 390 Port on behalf of Michael MacIsaac" > <LINUX-390@VM.MARIST.EDU on behalf of mike99...@gmail.com> wrote: > >> Hello list, >> >> We use vmcp extensively to issue CP commands. More and more I'm seeing >> this error: >> >> Error: Could not issue CP command: Cannot allocate memory >> >> I always use the --buffer=1M flag to be able to get the largest output. >> I've >> bumped up the VM size from 2 to 3 to 4GB, but still see it. We have some >> VDISK swap: >> # swapon -s >> Filename Type Size Used >> Priority >> /dev/dasda1 partition 99156 0 >> 100 >> /dev/dasdc1 partition 1057796 0 1 >> >> I reboot the system and it's gone. >> >> Has anyone seen this? Seems like it could be considered a bug - >> everything >> else on the Linux system seems fine. Or maybe I just need more swap? > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access instructions, > send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit > http://www.marist.edu/htbin/wlvindex?LINUX-390 > ---------------------------------------------------------------------- > For more information on Linux on System z, visit > http://wiki.linuxvm.org/ > ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
