Re: Very high memory usage with KVM

[Avi Kivity <avi@redhat.com>]

On 08/08/2009 03:54 AM, Daniel Bareiro wrote:
>> My guess is that it is due to poor swapping with pre-2.6.27 hosts.
>> 15 GB used out of 16GB total is just 6% reserve, which may be a bit
>> too low.  With a 2.6.27 host some small amount of memory would be
>> swapped out, before that you'd see thrashing.  Another way to check
>> is to drop one guest (or reduce total memory needed by 1GB) and see
>> if you get the same results or if things improve.
>>      
>
> I was testing in another equipment of similar characteristics with 4 VMs of
> 3.5 GiB of RAM on LVM and rather less the 16 GB of RAM in use in the host
> machine and 4 GIB available of the 8 GIB of swap, and after to update to
> KVM-88 the use of virtual memory improved enough.
>
> At the moment these are the statistics of memory usage:
>
> root@ss03:~# free
>               total       used       free     shared    buffers     cached
> Mem:      16463396    6700900    9762496          0    2805756     391884
> -/+ buffers/cache:    3503260   12960136
> Swap:      8319948          0    8319948
>
>
> Still I didn't update the kernel, so I am using KVM-88 with kernel
> 2.6.24-19. I would like to know if this can have some disadvantage, since
> in the official site of the project I was reading that kernel has to be
> 2.6.25 or newer to run the kvm 76 userspace (or any newer release).
>    

I think it's just luck; with kernel < 2.6.27 swapping behaviour will not 
be very good.

> The reason by which I didn't update kernel is because I was with some
> problems with the network interface on the host machine. Perhaps this
> problem is off-topic, but if somebody can help me with this, then it would
> contribute whereupon it can improve the KVM performance.
>
>    

Please take it to netdev, perhaps they can help you with this.

-- 
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