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Date: Wed, 22 Jun 2016 21:55:51 +0200
From: Peter Lieven <pl@kamp.de>
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Subject: Re: [Qemu-devel] Qemu and heavily increased RSS usage
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

Am 22.06.2016 um 12:56 schrieb Stefan Hajnoczi:
> On Tue, Jun 21, 2016 at 05:12:57PM +0200, Peter Lieven wrote:
>>  - We changed the coroutine pool to a per thread model. I disabled the pool. This seems
>>    to cut the max used RSS to about 150MB which is still a lot more than qemu-2.2.0
> The per-thread coroutine pools only grow when a thread creates/destroys
> coroutines.
>
> The QEMU main loop, iothread, and maybe vcpus should use coroutines.
> The numerous thread-pool worker threads should not use coroutines IIRC.
>
> Creating coroutines is expensive and the pools improve performance a
> lot.  Maybe you can make observations about how to manage pool size more
> efficiently for your VM?

I did not want to blame the coroutine pool. Its a good thing. I just wanted to
mention that we changed from a global pool (with a global mutex) to a thread
based pool. This might influence memory consumption. But the increased RSS
usage I observe is also there with disable coroutine pool.

What makes the coroutine pool memory intensive is the stack size of 1MB per
coroutine. Is it really necessary to have such a big stack?

Peter