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

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

* Michael Tokarev <mjt@tls.msk.ru> [2010-04-21 01:08]:
> 21.04.2010 05:58, Ryan Harper wrote:
> >* 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.
> []
> >Is that qemu-kvm 0.12.3 compiled from source? or using the distro
> >package?
> 
> (i'm not the OP, but we talked with him on irc about the issue)
> 
> It's a debian package of qemu-kvm.  There are a couple of cosmetic
> and unrelated patches applied to it, with one important to fix the
> large iovecs issue.  See
> 
>  http://git.debian.org/?p=collab-maint/qemu-kvm.git;a=tree;f=debian/patches;h=25ae313db327faa0559016e40fa6161018eb49f4;hb=caa82cbb176403e88128b4fe2698ff192ea10891
> 
> for the complete set of patches in there (it's debian/patches
> directory in http://git.debian.org/?p=collab-maint/qemu-kvm.git ,
> in v0.12.3+dfsg-4 branch).  The only interesting patch in there
> is the avoid_creating_too_large_iovecs_in_multiwrite_merge.patch
> one, the rest are not relevant.
> 
> >If you drop the -smp 4 part, you could also try plain qemu to eliminate
> >if there was a qemu-kvm merge issue.
> 
> So basically, upstream qemu now works as good
> as qemu-kvm for non-smp guests?

Not all of qemu-kvm features are upstream in qemu, but upstream qemu
supports kvm enough that it's worth testing to see if can't reproduce
there should provide some insight as to where the bug might be.  

> 
> >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.
> 
> There are only a few guests which are affected.  So far it is not
> really clear what differs them from others: a reinstall of a new
> guest with the same components and doing same functions will not
> necessary show the leak.

That is troublesome.  Are you saying if I install  lenny guest and do
the dd; cat I might not reproduce it?


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