Re: Guest memory usage

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Dietmar Maurer wrote:
> Hi Anthony,
>
> The problem is that memory always grows, even after rebooting the VM.
>   

When you start a VM, none of the memory for that VM has been reserved by 
Linux regardless of what you specify in the '-m' parameter.  Instead, as 
the guest starts to access memory, Linux begins to allocate memory for 
the guest.

free()'ing memory in the guest, rebooting the system, or anything else 
that you might thing should reduce memory consumption within the guest 
is meaningless to KVM.  One a KVM guest has accessed memory, that memory 
is permanently allocated.

There is, of course, an exception.  If the host system is low on memory, 
then Linux will request that KVM remove memory from the guest.  Again, 
this has nothing to do with what's going on in the guest, instead it has 
to do with what's going on in the host.

The Linux host is acting to balance out memory in the most appropriate 
way to maximize performance.  The guest will get as much memory as it 
needs until the host system starts getting low on memory.

If you want to know what much of the memory the guest is using, you need 
to ask the guest to tell you that.

Regards,

Anthony Liguori

>> The VSZ/RSS is correct.  What you're seeing is probably a mix 
>> of two things.  In the absence of MMU notifiers, not all 
>>     
>
> Sorry for asking stupid questions: Why are they absent? Isn't there a
> way
> to track memory usage? There are 'info tlb' and 'info mem' commands - 
> isn't it possible to construct better memory usage statistics whith that
> info?
>
> - Dietmar 
>
>
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