Re: madvise() not triggering page discard with MMU-notifiers

[Anthony Liguori <aliguori@us.ibm.com>]

Marcelo Tosatti wrote:
> Hi Anthony,
>
> On Mon, Aug 18, 2008 at 05:04:25PM -0500, Anthony Liguori wrote:
>   
>> Attached is an updated migration patch.  It does not appear, however,  
>> that madvise() is triggering discarding of pages even with an  
>> MMU-notifier enabled kernel.  I take it that this is because we're still  
>> holding a reference count to the page when it is in the shadow page  
>> table?  Any ETA on when this will change?
>>     
>
> Shadow references should be dropped via kvm_unmap_rmapp -> rmap_remove. 
>
> So the symptom is that RSS for the task does not decrease accordingly to
> the ballooned down size?
>   

Correct.  I run a workload in the guest to touch all of memory, watch 
the RSS size go up to 1G, then balloon down to 512mb.  I don't see the 
RSS size reduce at all though.

This is not the case when just using QEMU.  When I get a chance to 
debug, the next step will be to annotate the code to see whether 
rmap_remove is actually being invoked on madvise().

Regards,

Anthony Liguori