drop_caches ...

[Markus <M4rkusXXL@web.de>]

Hello!

I have a small problem. Maybe its just a misunderstanding but I cant 
solve it.

I think that writing "3" to drop_caches should drop all buffers and 
caches which are already written. So its recommended to put a "sync" 
infront of it.
So I did "free -m ; sync ; echo 3 > /proc/sys/vm/drop_caches ; free -m"
And it gave me:
             total       used       free     shared    buffers     
cached
Mem:          3950       3922         28          0          1        
879
-/+ buffers/cache:       3041        909
Swap:         5342        205       5136
             total       used       free     shared    buffers     
cached
Mem:          3950       3907         43          0          0        
864
-/+ buffers/cache:       3041        908
Swap:         5341        206       5135

So the buffer was 1 and is 0 afterthat. But cached is at 879 MB before 
and is still 864 MB (!!!) after that!

I am at swappiness=0 and when I remove and readd one swap-partition 
after another (so there is always swap). It will keep the cached and 
put the swapped memory on other swaps?!

I _think_ thats not the way it should go?

It would be really kind if someone could explain that issue and 
what "cached" is at all!

Have a nice day...
Markus

PS: Please CC me as I am not subscribed.