How to reduce cached memory?

[Chris Tyler]

On Fri, 2009-02-06 at 23:57 +0100, Joshua C. wrote:
> I have kde 4.2 and f9. After 2+ hours on my computer it has about
> 1,4GB cached memory. I don't see him releasing this memory after time.
> I know it comes from the apps being open but it seems the kernel
> "never" releases the memory after the app terminates. How to make the
> kernel free this memory? I've seen similar cases with kde 3.5.10 and
> f8 and f7. I know kde eats memory but this is too much. Who caches so
> much of it? Why?
> 
> The mashine has 2,6 GB RAM (still x86) and 512mb swap which is rarely
> used (~ 50mb at most) and combined cached + app memory totals about 2
> gb.

Hi Joshua,

Memory is being used for cache basically because it's not being used for
anything else. The kernel will gladly use that memory for other purposes
when it's needed -- but until then, there's no harm in keeping disk data
around in otherwise-unused memory just in case it's needed later.

This is why the "free" command shows a "-/+ buffers/cache" line, which
shows you what the memory picture is without the cache (i.e., the memory
that is truly available when needed):

  $ free
               total     used    free  shared buffers cached
  Mem:       4061388  3796632  264756       0  259244 570224
  -/+ buffers/cache:  2967164 1094224
  Swap:      4194296  2092276 2102020


-Chris