Re: [Qemu-devel] [Question] Qemu's Heap Becomes Very Large and Never Reduce Down

[Xulei (Stone)]

> On Wed, Nov 15, 2017 at 02:18:55PM +0100, Paolo Bonzini wrote:
> > On 15/11/2017 04:14, Xulei (Stone) wrote:
> > > Hi, guys
> > >
> > > I met a strange problem, with qemu 2.8.1:
> > > qemu consumes too many heap memory after several operations and can
> > > not release them anymore:
> > > hot pulg/unplug disk & net, vnc connect/disconnect, guestOS reboot, etc.
> >
> > Try with newer QEMU; until recently we used a lot of memory at
> > startup, but it was improved in 2.11.
> >
> > However, I think Anthony also had a patch adding a malloc_trim call in
> > the RCU thread, which improved memory usage.  Anthony, do you know if
> > this is still necessary in 2.11?
> >
>   Hello Paolo,
> 
>   Last time, when you traveled in BeiJing, we talked about this malloc_trim()
>   solution in RH office. At that time, you asked me to send this patch to
> upstream.
>   I can try this patch in the newest Qemu version if you regard this solution 
> is
>   suitable.
> 
>   I also want to look for other more better solution, but there are some
> urgency
>   tasks interrupt me.
> 
>   In fact, Anthony also have some other solutions for heap memory deduction
> in
>   our intel ClearContainer.
> 

Thanks for reply！
 
I'll test my cases with the upstream qemu ~

In fact, I'd like treat this problem as an unawareness bug. Because:
1) This problem happens NOT during the bootup phase but after several 
operations.

2) It happens at a low probability, 5 VMs of 10 hosts * 20 VMs (10 hosts, each 
runs 20 VMs).

3)Once it happens, we can NOT deduct the heap memory through unplugging all 
disks & nets, 
disconnecting VNC, and rebooting guestOS.

4)Refer to Stefan's advice, I have already isolated my tests that do only one 
operation persistently 
one time. The heap memory does not grow up very high.

I may think specific operation sequence can trigger this BUG.
I'll do some more tests, and supply more useful information for YOU.

BTW, I am now also following intel ClearContainer and Hyper project, I think 
they are awesome.

>   Regards,
> 
>   Yang Zhong
> 
> > Thanks,
> >
> > Paolo