On Aug 12, 2004, at 1:15 PM, David Boyes wrote:
I've always been under the impression that the best configuration for Linux/390 guest swap is to make the virtual machine storage as large as it SHOULD need under normal operating conditions, and give the guest practically NO swap.
Not quite. The idea is to keep the virtual machine size as small as possible, *and* allow Linux to swap via the most efficient method possible if it's necessary. Linux dies horribly if it hits a burst of activity and can't find enough swap to handle the load.
"Dies horribly" is a bit extreme. But, yes, eventually the kernel will just start picking processes to kill, and that's never good. Which is why you need to budget VDISK for the common case when the machine suddenly needs a few more megabytes. Depending on the workload, you may also need to budget real DASD (or more VDISK if you can spare it) for giant spikes in RAM usage.
You can then either adjust the virtual machine size to avoid swapping, or you can accept some amount of swapping and keep the maximum working set size for the virtual machine small, and expend the real storage on VDISK for swap, which gets allocated only if it's really needed.
David and I are of course arguing for the second, since this prevents caching a lot of file I/O in the Linux guest, and swapping to VDISK is not a big performance hit.
Adam
---------------------------------------------------------------------- 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
