Ok, so the swap behavior is: look for allocated but reuse-able swap blocks in the full higher/est priority swap partition before starting to allocate from lower priority swap partition? swap allocation stays within the higher priority (but purposely smaller) partitions as long as it finds a free or a reusable block?
-------------------------------------------------------- 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 reply e-mail and delete the e-mail from your system. -----Original Message----- From: Linux on 390 Port [mailto:[EMAIL PROTECTED] On Behalf Of Mark Wheeler Sent: Friday, October 12, 2007 10:25 AM To: [email protected] Subject: Re: high water mark for swap space used? > Rob van der Heij said: > Right. So you make an educated guess for what you think you need, and > define an additional large VDISK as the next level of swap. You use > the performance monitor to alert you when that next level of swap gets > used (which means you overflowed the first one, so that should be made > larger). > You also need other metrics from your performance monitor to > understand when the first swap disk is too large (that's when z/VM > needs to page-in the VDISK frequently). So the right size of swap disk > depends both on application requirements and on available resources in > z/VM. Because a change in VDISK size changes the behavior of the > application, you can not really predict these things. You need to > measure and act on that. > The predomininant recommendations I've seen say allocate two VDISK swap areas, one with a "best guess" size, and a 2nd lower-priority, large swap area. Since Linux supports up to eight, I define 'em all, starting with a small, high-priority VDISK, then doubling each successive disk thereafter, which provides a great deal of resiliance in case I underestimate the requirement, or an unexpected spike occurs. If I start seeing pages on more than the first two or three, then I know it's time to increase my virtual machine size. On the flip side, if I see that none of the swap volumes are used, it may be time to reduce the virtual machine size. Here's some info from one of my current machines: # /sbin/swapon -s Filename Type Size Used Priority /dev/dasds1 partition 980 980 -1 /dev/dasdt1 partition 1972 1972 -2 /dev/dasdu1 partition 3952 3952 -3 /dev/dasdv1 partition 7920 7920 -4 /dev/dasdw1 partition 15852 13440 -5 /dev/dasdx1 partition 31720 10860 -6 /dev/dasdy1 partition 63456 240 -7 /dev/dasdz1 partition 126924 0 -8 <snip> Mark L. Wheeler ---------------------------------------------------------------------- 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
