Why should it ever be acceptable for someone to sit down in the morning to a machine with 4GB+ RAM and have things like a volume OSD take tens of painful seconds to swap in because the night before the machine ran 'updatedb' and the system decided to swap out a few bits of "unused program memory" with a useless cache of the entire disk index?
Then set /proc/sys/vm/swappiness to 0 and be happy.
But actually linux never ejects pages to swap just for the cache. It will only eject pages for memory pressure, which, when freed, can leave extra room for cache. But it won't eject the pages in the first place for the cache.
Because updatedb isn't inherently useless, but rather that file system caching (especially for pages read once) shouldn't eject application pages from RAM to disk.
Being able to run locate and have it quickly return an accurate result is useful at times. I just don't want it paging my entire session out to disk every night in order to do that.
