Re: [Xen-devel] qemu-system-i386: memory leak?

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

On 02/01/13 16:58, Ian Campbell wrote:
> On Mon, 2012-12-31 at 13:06 +0000, Roger Pau Monnà wrote:
>> On 26/12/12 11:46, Maik Wessler wrote:
>>> Hi all,
>>>
>>> I am using xen-4.2-testing.hg on debian 6.0.6 (x86_64) with Kernel
>>> 3.4.15 (tmem enabled).
> 
> Why 3.4.15? Would be good to either use the distro kernel or keep up
> with the upstream stable branch.
> 
>>  Problem is that the /usr/lib/xen/bin/qemu-system-i386
>>> use more and more memory. After one week uptime (depends on memory) the
>>> machine starts to swap...
> [...]
>>>  total           424016K
>>>
>>>
>>> Can anyone help?
>>
>> I've just posted a bug fix for a memory leak in Qemu Xen PV disk
>> backend, you can take a look at the patch at:
>> http://lists.nongnu.org/archive/html/qemu-devel/2012-12/msg03677.html.
> 
> The pmap doesn't appear to show any open backing devices for a disk so
> I'm guessing this isn't in use?

Qemu doesn't use mmap to open the disk file, so I guess it's normal that
the backing file is not shown in the pmap trace (that's more or less the
same map I get from qemu with one qdisk attached to a DomU).

> Given that this is a PV guest and I can see -nographic on the qemu
> command line I'm not what qemu is doing -- can we see the guest
> configuration please? "xl -vvv create" logs would be useful too.
> 
>> There's also a memory leak in the linux gntdev device which is used by
>> Qemu, you should also take a look at the following linux kernel patch
>> http://git.kernel.org/?p=linux/kernel/git/konrad/xen.git;a=commit;h=a67baeb77375199bbd842fa308cb565164dd1f19.
>>
> 
> This is possible.
> 
> If it doesn't turn out to be this then one approach might be to arrange
> to run qemu under valgrind for a little bit and see if anything springs
> out.
> 
> You'd probably need at least r13081 of Valgrind's SVN trunk to remove
> all the noise due to hypercalls.

I've run Qemu blkback for PV guests (qdisk) under Valgrind, and found
only the leak that the above patch fixes.


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