This is interesting. Having 2TB of page space in test/dev I'm sure we have some potential space savings if this could be done across all dev/test servers...
However, you'd really want to do this carefully and it might not even be practical if linux itself didn't drive this diag. If done outside (ala Rob's cmmflush), you'd need to swapoff the disk so that you first make linux clean it up and to prevent it from putting more on there. Swapoff of a full 2G disk takes a very long time (more than 30 minutes IIRC). It probably drives up the page rate while that is going on as well. And if you've done the swapoff, no big deal to just add a vary off, detach, define, mkswap, swapon to your script in lieu of a diag to do it. Probably would need to stagger this activity if you have a lot of servers on a single box. As often as we have to reboot or IPL VM for security patching, HW work, and other maintenance anymore, here anyway it gets cleaned up fairly often. So I can see why VM development would reject it since they'd really need Linux development to make use of it and Linux development might not be that interested if it's never going to be accepted into the kernel since the x side doesn't swap well anyway and adding cheap memory is the solution there. Actually, maybe it is here too. Making the vdisks smaller and memory size bigger and running CMM often might accomplish what is desired? -----Original Message----- From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Barton Robinson Sent: Wednesday, December 09, 2015 12:13 PM To: LINUX-390@VM.MARIST.EDU Subject: Re: [LINUX-390] Status of VDISK after swap space usage My request to get this fixed was rejected by ibm several years ago. The problem is that even though linux doesn't have anything on the vdisk, z/vm still has to back it. I asked for a diagnose as we do with real storage - a way for Linux to tell z/vm the page no longer needs backing. So after the swapoff, can you detach the vdisk? That's the only way with current technology to tell CP to free it up. On 12/9/2015 12:05 PM, Mrohs, Ray (JMD) wrote: > Hi, > Our environment consists of SLES 11.4 servers under VM 6.2. > > Sometimes we have misbehaving Linux applications that dip heavily into the > SWAPGEN configured swap space. After things settle down, Linux never lets go > of the space until we issue a swapoff -a, and swapon -a. Of course I do this > after making sure that we have sufficient free memory available in that > server. The reported swap use then effectively returns to zero. But it seems > like nobody tells VM because the VDISK being retained in memory for that > virtual machine, as reported by Velocity, is consistent with the maximum swap > space that was used, something on the order of 190K pages, and it never > decreases even though the Linux swap use stays at zero. Does VM ignore this > until it hits a memory use threshold, or does Linux not clean up well after > itself, or maybe we are missing something else? We are trying to avoid a > "just reboot it" action. > > This is our typical swap disk entry in fstab: > /dev/disk/by-path/ccw-0.0.0105 swap swap > defaults 0 0 > > Ray Mrohs > Lockheed Martin Corporation > Service Delivery Staff > Infrastructure Operations > ray.mr...@usdoj.gov > 202 307-6896 > > ---------------------------------------------------------------------- > 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/ ---------------------------------------------------------------------- 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/
