Hi Well this is not something I would do in my shop. Not having swap available for Linux is just asking for trouble. One reason is that you really want to size your guests in such a way that they use just a trickle of swap this allows you to size a guest in terms of memory defined to the guest to allow z/Linux to maximize the handling of the memory and from a performance standpoint you really want it to be VDISK.
One of the things that makes running z/Linux under VM so appealing is the ability to take a server running in Solaris let's say that has 20G and cut that in half or more when it is migrated to z/Linux under VM. To do this you need to have flexibility when it comes to paging and swapping for the guest. Thank You, Terry Martin Lockheed Martin - Citic z/OS and z/VM Performance Tuning and Operating Systems Support Office - 443 348-2102 Cell - 443 632-4191 -----Original Message----- From: Linux on 390 Port [mailto:[email protected]] On Behalf Of Mrohs, Ray Sent: Monday, June 28, 2010 10:21 AM To: [email protected] Subject: Re: Memory use question This led me into an interesting area. I just set a couple of our test servers to run without swap space. This could put a bigger paging load on VM at times, but then again simplifying the Linux configuration and having VM do the heavy lifting are both good selling points. I'm also thinking about when I eventually hand this work over to someone else. Not having to explain v-disks and the interplay of paging and swapping between the hypervisor and guests could avoid confusion and mistakes being made. Of course Linux memory utilization becomes critical, and we can watch it with something like this and adjust virtual CP storage accordingly: ps -eo pmem | awk '{pmem += $1}; END {print "pmem = "pmem"%"}'; Right now our biggest WebSphere server is running comfortably at ~60% memory used, out of 2G. Is anyone else running swapless servers big or small? If swap space is considered a safety valve to keep a server up, then I would just as soon put it on real DASD, and avoid its use with proper memory sizing. Ray > -----Original Message----- > From: Linux on 390 Port [mailto:[email protected]] On > Behalf Of Marcy Cortes > Sent: Thursday, June 24, 2010 10:34 AM > To: [email protected] > Subject: Re: Memory use question > > So with swappiness higher, Linux is making decsions to > preemptively move something from memory to vdisk. Well, your > vdisk is in VM's pageable memory too. > So moving something from one piece of VM memory to another > piece of VM memory means both parts will have to become > resident. The source page probably had already been paged > out by VM if Linux hadn't been using it recently and the > vdisk page may not have even existed or if it did since it > had been used before, it was likely paged out too. > > Marcy ---------------------------------------------------------------------- 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/ ---------------------------------------------------------------------- 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/
