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SubjectRe: drop_caches ...
Hi Markus,

On Wed, Mar 04, 2009 at 10:57:33AM +0100, Markus wrote:
> 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!

The memory mapped pages won't be dropped in this way.
"cat /proc/meminfo" will show you the number of mapped pages.

Thanks,
Fengguang


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