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 marcy.d.cor...@wellsfargo.com "This message may contain confidential and/or privileged information. If you are not the addressee or authorized to receive this for the addressee, you must not use, copy, disclose, or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation." -----Original Message----- From: Linux on 390 Port [mailto:linux-...@vm.marist.edu] On Behalf Of Mrohs, Ray Sent: Thursday, June 24, 2010 5:53 AM To: LINUX-390@vm.marist.edu Subject: Re: [LINUX-390] Memory use question > -----Original Message----- > From: Linux on 390 Port [mailto:linux-...@vm.marist.edu] On > Behalf Of Marcy Cortes > Sent: Wednesday, June 23, 2010 3:45 PM > To: LINUX-390@VM.MARIST.EDU > Subject: Re: Memory use question > > Rob mentioned the vm.swappiness setting and he and I have had > a lot of discussions about that one. You do want to probably > set that to zero on a WAS server (and probably others). It's > recommended in this WAS tuning paper too > http://download.boulder.ibm.com/ibmdl/pub/software/dw/linux390 > /perf/ZSW03132USEN.PDF I have trouble seeing whether using memory or v-disk in memory is more effective, though I might have read that VM needs to page more for large seldom referenced v-disk spaces. My natural inclination is to use RAM first and swap last, perhaps based on outdated notions. Anyway I set swappiness to zero. The publication also seems to recommend a heap size that is ~70% of available memory. In our case that would equal 1400M which is 400M more than our current max. setting. Ray ---------------------------------------------------------------------- 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/
