[lug] "Cache" under linux

Michael D. Hirsch mhirsch at nubridges.com
Wed Mar 12 12:42:22 MST 2003

On Wednesday 12 March 2003 01:54 pm, Eric Peers wrote:
> When I run top, I notice that I have very little free
> memory in my system, and yet the process memory usage
> count does not reflect this used memory.
> So I found a command called free:
> crampon> free
>              total       used       free     shared
> buffers     cached
> Mem:        998748     899816      98932          0
>  134052     558556
> what is this "cached" memory usage? Is it for virtual
> memory? is there a way to control the amount of it
> which is used for paging? Should I even worry about
> it? (because it seems to grow in size the longer I use
> my system).

Don't worry--this is normal.  If you aren't actively using some memory 
Linux will use if for the disk cache.  If a process needs it it will get 
freed up instantly.

Of more interest is the second line from free that you didn't print.  
Here's mine:
1012] 3rdParty>free
             total       used       free     shared    buffers     cached
Mem:        998692     978660      20032          0      36420     207428
-/+ buffers/cache:     734812     263880
Swap:      2040244     777068    1263176

The first line shows only 20M free, but the seconf line points out that 
there is really 263M free.  Note that this is free+buffers+cached from the 
first line.


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