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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: Fri, 24 Jun 2016 10:11:09 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

Am 24.06.2016 um 06:10 schrieb Paolo Bonzini:
>>> 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 the right place.
> Yes, you can do that.  Just make it call the function without locks, for
> a quick PoC it will be okay.

Unfortunately, it leads to immediate segfaults because a lot of things seem
to go horribly wrong ;-)

Do you have any other idea than reverting all the rcu patches for this section?

I'm also wondering why the RSS is not returned to the kernel. One thing could
be fragmentation....


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