Re: Huge memory leak in virtio, see kvm-Bugs-2989366

[Ryan Harper <ryanh@us.ibm.com>]

* Leszek Urbanski <tygrys@moo.pl> [2010-04-20 17:37]:
> Hi,
> 
> this is a follow-up to bug 2989366:
> 
> https://sourceforge.net/tracker/?func=detail&atid=893831&aid=2989366&group_id=180599
> 
> after extensive debugging with the guys on #kvm it turns out that the leak is
> in the qemu-kvm userland process, in virtio-blk.
> 
> A summary of my setup is described in the bug report above.
> 
> The affected guests have a common load profile: frequent sequential I/O on
> large (~ 2 GB) files.
> 
> I tried switching off or changing almost all options in my qemu command
> line and the only option that makes a difference is -drive if=virtio.
> 
> When an affected guest is run with virtio drives the qemu-kvm process starts
> leaking immediately after startup and grows (for the most heavily leaking
> guests) by ~ 1 GB RSS for every ten hours (and keeps growing until OOM).
> 
> With -drive if=ide or scsi, it doesn't leak at all.
> 
> A diff of /proc/<pid>/maps of an affected qemu-kvm at startup and after
> 1.5 hrs:
> 
> -039b9000-5ccd0000 rw-p 00000000 00:00 0
> +039b9000-65803000 rw-p 00000000 00:00 0
> 
> (a heap leak?)
> 
> I'm willing to debug further. The problem is 100% reproducible.

Is that qemu-kvm 0.12.3 compiled from source? or using the distro
package?

If you drop the -smp 4 part, you could also try plain qemu to eliminate
if there was a qemu-kvm merge issue. 

Also, if you switch to a different guest do you still see the same leak?
This should help determine if the virtio-blk front end is part of the
issue.


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com