On Sunday 06 March 2005 23:10, Hans Witvliet wrote:
I allready though so, For most "normal" situations, sysadmins consider swap nowadays more as a protection meganism against kernel panics.
Used to be different. I recall the days (on a dec vax/vms 780) and several hundred people working on it, and on piek moments during the week, most of us were watching which users were swapped out ;-)) At that time "swapped/paged-out" was a fact of life. But since then, CPU, cache and mem-speed have rissen 1000-fold; while "background" -memory, or disks in general perhaps 10 or 20-fold. So the effect of a process being swapped out of main-memory is felt much more.
At the HP-UX training classes we were told if a system was using swap intens and for a longer period, one should prepare for several things: -Complaining users (bad system response) -Looking for bad code -Start procedures for buying additional memory
So over-commiting your memory (thus swapping) is something to avoid at all costs.
Only perfect sense for swapping a processes on purpose, might be in a cluster environment, to re-distribute cpu-load....
Swapping has other uses. Swapping rarely used data from main internal memory to free up space for disk cache and read-ahead buffers can improve performance. This is why you can sometimes see swap usage even though you have a gigabyte free.