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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 23:28:33 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

Am 23.06.2016 um 18:53 schrieb Paolo Bonzini:
> On 23/06/2016 18:19, Peter Lieven wrote:
>> Mhh, so your idea could be right. But what to do now? The introduction
>> of RCU obviously increases the short term RSS usage. But thats never
>> corrected as it seems.
>> I see this behaviour with kernel 3.19 and kernel 4.4
> If it's 10M nothing.  If there is a 100M regression that is also caused
> by RCU, we have to give up on it for that data structure, or mmap/munmap
> the affected data structures.

If it was only 10MB I would agree. But if I run the VM described earlier
in this thread it goes from ~35MB with Qemu-2.2.0 to ~130-150MB with
current master. This is with coroutine pool disabled. With the coroutine pool
it can grow to sth like 300-350MB.

Is there an easy way to determinate if RCU is the problem? I have the same
symptoms, valgrind doesn't see the allocated memory. Is it possible
to make rcu_call directly invoking the function - maybe with a lock around it
that serializes the calls? Even if its expensive it might show if we search at 
right place.


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