In both environments smaller virtual machines are easier to dispatch and are better guests as far as the hypervisor is concerned. However- on x86 the hypervisor has to do a lot more work to virtualize the IO, and the platform in general has to do a lot more work for IO, and so everyone adds system memory to use as a local buffer to mask the costs of IO.
You can certainly allocate s390x guests exactly like you do x86_64 guests, but you will end up with Linux systems that cache their file systems aggressively and make everything unpleasant for all guests. One way of working around this while still giving the application teams what they are familiar and comfortable with is to use the cmm driver to tell the Linux kernel to give memory back to the hypervisor. The OS still sees 8 GB, but you can tell the driver to give <integer> number of 4K pages back, and prevent the guests from piddling away real memory on file system cache. Check the Linux Device drivers book at http://www.ibm.com/developerworks/linux/linux390/documentation_dev.html for docs on the cmm module. The better approach though is to incentivize the developers to be happy with the smaller default virtual machine size somehow. Make it cheaper than the x86 equivalent, make it self service, make it more appealing somehow. I have had success by committing to the development teams inside IBM that are doing ports to s390x that I will examine their utilization and ensure that they are not having a bad experience, and use some performance toolkit alerts to get notifications when the virtual machines start doing IO to their swap devices - that is my signal that those guys legitimately need more memory and I can arrange to get that configured for them. On Wed, Apr 6, 2016 at 10:41 AM, Levy, Alan <[email protected]> wrote: > Hopefully someone can resolve an argument that I'm having with a colleague. > > We are competing with the distributed side which using VMware to create > sles linux servers. They create servers with 8G of memory and 8G of swap > for EVERY server. My colleague wants to follow this architecture for our > zvm servers (giving them 8G of memory and 8G of vdisk). > > My opinion is to give them a default of 2G of memory and 2G of vdisk and > increase the main memory as needed. > > My colleague is concerned that if we give them less, they will always go > to the distributed side since they give more. I am concerned about giving > so much memory might negatively impact our zvm systems. > > > > > ________________________________ > > This e-mail, including any attachments, may be confidential, privileged or > otherwise legally protected. It is intended only for the addressee. If you > received this e-mail in error or from someone who was not authorized to > send it to you, do not disseminate, copy or otherwise use this e-mail or > its attachments. Please notify the sender immediately by replying to this > e-mail and delete the e-mail from your system. > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access instructions, > send email to [email protected] 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/ > -- Jay Brenneman ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] 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/
