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

From: Peter Lieven
Subject: Re: [Qemu-devel] Qemu and heavily increased RSS usage
Date: Thu, 23 Jun 2016 17:02:23 +0200
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Am 23.06.2016 um 17:00 schrieb Dr. David Alan Gilbert:
* Peter Lieven (address@hidden) wrote:
Am 21.06.2016 um 15:18 schrieb Dr. David Alan Gilbert:
* Peter Lieven (address@hidden) wrote:

while upgrading from Qemu 2.2.0 to Qemu 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 (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:
OK, while 10MB is bad, I'm more interested in where your other 270MB have gone 
- hopefully
it's not 27 separate 10MB chunks!

I'm trying to figure out the exact commits, but its very hard to bisect so far. 
This is the
first commit that really introduces an easy to reproduce RSS increase. Maybe 
this is the root
cause. I don't know.


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