>> Then why not have a really big swap file? If swap is useful as a >> second layer of caching behind RAM, why doesn't everyone with some >> extra hard drive space have a 100GB swap file? >> > You've not understood what I said, I think. Swap is not useful as > filesystem cache. Swap is as efficient (probably a little less) than > the files on the disk. It's RAM that's efficient as filesystem cache. > > Where swap comes in is the kernel can swap out pages from "stale" > processes, and reclaim the RAM as filesystem cache.
That all makes perfect sense, but if a small swap is good and a large swap is not any better, I'm missing something. Maybe the pages from stale processes never total more than a small amount? I don't see how that could be. - Grant > Think of it this way: You have a house with an attic. Now the attic is > not as "efficient" as say, the middle of your living room. You have a > Christmas tree, but you only use that Christmas tree maybe once a year. > Now it's much more efficient to keep that Christmas tree in the attic > for 11 months of the year and use that reclaimed space in your living > room for.. say a coffee table. Then, when you need that Christmas tree > in December, you pull it out of the attic and maybe put the coffee table > up in the attic for a month. > > The Christmas tree represents a process that's just sitting out there > doing not much half the time, but taking up space. The space in your > living room is RAM, and the space in your attic is swap. The coffee > table is filesystem cache.
