>> So swap isn't treated exactly like RAM. It actually has special >> handling in Linux which makes it beneficial to have on almost any >> Linux system? According to Alan, things get very bad when a Linux >> system hits swap. How can behavior like this be beneficial: >> >> "When a linux machine hits swap, it does so very aggressively, there >> is nothing nice about it at all. The entire machine slows to a >> painstaking crawl for easily a minute at a time while the kernel >> writes pages out to disk, and disk is thousands of times slower than >> RAM. >> > This is not entirely true. There's regular swapping and there is > "thrashing". Thrashing is indicative of a memory-starved system, i.e. > when many processes are trying to access memory, but there just isn't > enough and the system is frantically swapping in/out. I'm talking about > your normal day-to-day swapping that you probably don't even notice. > >> It gets so bad that you can't even run a shell properly to try and see >> what's going on and kill the actual memory hog." > > Again, that is thrashing. I'm talking about "normal" swappage. Dont > throw the baby out with the bath water. > >> Also, aren't you likely to wear out your hard disk sooner using swap? > > Is this coming from someone who uses Gentoo linux, which is constantly > downloading/compiling/linking object files? Syslog and other loggers > writing everything under the sun to a log file. Backups, journal > writes, database transactions, etc. Compare how many disk transactions > take place during your normal Gentoo usage versus a few megabytes > here/there being swapped in/out. Again, I'm talking about regular > swapping, not "oh my god I has no RAM and my hard drive won't stop" > Even so, we're talking about modern drives here. This isn't the 1960s.
If I understand correctly, an out-of-memory condition that would lock up a system without swap, will cause it to thrash with swap. A remote system of mine was locked up for many hours due to running out of memory without swap. If I had enabled swap, the system would have thrashed for those hours? - Grant
