Re: [Qemu-devel] Tracking hugepages usage

[Vladyslav Drok]

On Thu, Jun 1, 2017 at 2:55 PM, Vladyslav Drok <address@hidden> wrote:

>
>
> On Thu, Jun 1, 2017 at 1:56 PM, Andrey Korolyov <address@hidden> wrote:
>
>> On Thu, Jun 1, 2017 at 1:38 PM, Vladyslav Drok <address@hidden>
>> wrote:
>> > Hello qemu community!
>> >
>> > I come from openstack world, and one of our customers complains about an
>> > issue with huge pages on compute nodes. From the "virsh frepages --all"
>> and
>> > "cat /proc/meminfo", they see that 4 huge pages are consumed:
>> >
>> > http://paste.openstack.org/show/611186/
>> >
>> > In total there are 239 1G pages, 120 in numa node 0, and 119 in numa
>> node
>> > 1. There are no VMs running at this point.
>> >
>> > When trying to find out what consumes the 4 1G huge pages from node 0, I
>> > was suggesting "grep 1048576 /proc/*/numa_maps" to find out which
>> processes
>> > are using 1G pages, but in this particular case it shows no processes.
>> > While when some VM is running, I can see the qemu process that's
>> consuming
>> > huge pages, numa_maps reports the correct amount of pages,
>> corresponding to
>> > what has been requested for the VM's RAM.
>> >
>> > Are there any recommended ways for trying to track what consumes these 4
>> > "lost" pages? (I might be a bit slow providing more info, as I don't
>> have
>> > access to this environment :( )
>> >
>> > Thanks,
>> > Vlad
>>
>> Could you please try to walk against /proc/[0-9]/smaps to check that
>> these pages are not claimed by any process?
>>
>
> Thanks for the suggestion! Will provide the results as soon as I have it.
>
> So, here (in the attachment, is is a bit lengthy so, sorry, was not able
to use paste :)) is an output of ps -F and smaps for processes that have
any entry with KernelPageSize: 1048576 kB. In this case, there are two
instances running on this compute node, 16 GB and 32 GB. The usage reported
by qemu processes seems to report huge page count correctly. In case of
ovs-vswitchd process, I'm not sure how to interpret the output, as if I
just add up the number of pages used by that, it is much bigger than it's
reported as used, any hint on that would be much appreciated :) Though the
ovs-vswitchd process is run with --huge-dir /mnt/huge_ovs_2M which is where
2 mb pages are mounted, so I supposed it should not use the 1G pages.

I'll also try to request the output for a compute that does not have any
instances running but still having some pages used, so the problem is a bit
more clear.

Thanks,
Vlad

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