Re: [Qemu-devel] Qemu and heavily increased RSS usage

[Peter Lieven <pl@kamp.de>]

Am 21.06.2016 um 15:18 schrieb Dr. David Alan Gilbert:
> * Peter Lieven (pl@kamp.de) wrote:
>> Hi,
>>
>> while upgrading from Qemu 2.2.0 to Qemu 2.5.1.1 I noticed that the RSS memory usage has heavily increased.
>> We use hugepages so the RSS memory does not include VM memory. In Qemu 2.2.0 it used to be ~30MB per vServer
>> and increased to up to 300 - 400MB for Qemu 2.5.1.1 (same with master). The memory increases over time, but seems
>> not to grow indefinetly. I tried to bisect, but had no result so far that made sense. I also tried valgrind / massif, but
>> valgrind does not see the allocation (at least at exit) and massif fails to rund due to - so it pretends - heap corruption.
>>
>> Any help or ideas how to debug further would be appreciated.
> I think I'd try stripping devices off; can you get a similar difference
> to happen with a guest with no USB, no hugepages, no VGA and a simple
> locally stored IDE disk?
>
> If you're having trouble bisecting is it possible it's a change
> in one of the libraries it's linked against?
>
> There was someone asking the other day on #qemu who had a setup that
> was apparently using much more RAM than expected and we didn't
> manage to track it down but I can't remember the version being used.

I currently trying to track the increased usage from release to release. The first increase of RSS usage from ~25MB to ~35MB directly
after machine setup is introduced by this patch:

commit ba3f4f64b0e941b9e03568b826746941bef071f9
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Wed Jan 21 12:09:14 2015 +0100

     exec: RCUify AddressSpaceDispatch

     Note that even after this patch, most callers of address_space_*
     functions must still be under the big QEMU lock, otherwise the memory
     region returned by address_space_translate can disappear as soon as
     address_space_translate returns.  This will be fixed in the next part
     of this series.

     Reviewed-by: Fam Zheng <famz@redhat.com>
     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

@Paolo, @Fam, any idea?

Thanks,
Peter