Linux Ate My RAMDon't panic. Your RAM is fine
What's going on?
Linux is borrowing unused memory for disk caching. This makes it looks like you are low on memory, but you are not! Everything is fine!
Why is it doing this?
Disk caching makes the system much faster! There are no downsides. It does not take memory away from applications in any way, ever!
What if I want to run more applications?
If your applications want more memory, they just take back a chunk that the disk cache borrowed. Disk cache can always be given back to applications immediately! You are not low on ram!
Do I need more swap?
No, disk caching only borrows the ram that applications don't currently want. It will not use swap. If applications want more memory, they just take it back from the disk cache. They will not start swapping.
How do I stop Linux from doing this?
You can't disable disk caching. The only reason anyone ever wants to disable disk caching is because they think it takes memory away from their applications, which it doesn't! Disk cache makes applications load faster and run smoother, but it NEVER EVER takes memory away from them! Therefore, there's absolutely no reason to disable it!
How do I see how much free ram I really have?
To see how much ram is free to use for your applications, run free -m and look at the row that says "-/+ buffers/cache" in the column that says "free". That is your answer in megabytes:
$ free -m
total used free shared buffers cached
Mem: 1504 1491 13 0 91 764
-/+ buffers/cache: 635 -> 869 Swap: 2047 6 2041
If you don't know how to read the numbers, you'll think the ram is 99% full when it's really just 42%.