Regarding fine tuning my explanation about what system does de actual mounting of Hugepages, you’re probably right…. Thanks for the correction.

On upstart systems (like Ubuntu) the mounting of Hugepages is done by the init script qemu-kvm.conf

Van: G. Richard Bellamy [mailto:rbellamy@pteradigm.com]
Verzonden: zondag 1 februari 2015 0:02
Aan: Dominique Ramaekers
CC: libvirt-users@redhat.com
Onderwerp: Re: [libvirt-users] HugePages - can't start guest that requires them

Yeah, Dominique, your wiki was one of the many docs I read through before/during/after starting down this primrose path... thanks for writing it. I'm an Arch user, and I couldn't find anything to indicate qemu, as its compiled for Arch, will look in /etc/default/qemu-kvm. And now that I've got the right page size, the instances are starting...

The reason I want to use the page element to the hugepages directive is that I want to target a numa node directly - in other words, I like the idea of one VM running on Node 0, and the other running on Node 2.

Your comment about libvirt taking care of the hugepages mount isn't consistent with my reading or experience - on a systemd-based system, systemd takes care of the hugetlbfs mount to /dev/hugepages, and the libvirt builds the /dev/hugepages/qemu... directory structure. At least that's what I've seen.

-rb

On Sat, Jan 31, 2015 at 11:43 AM, Dominique Ramaekers <dominique.ramaekers@cometal.be> wrote:

Did you create a mount for the hugepages? If you did, that's maybe the problem. I did that also at first but with libvirt it isn't necessary and in my case, it broke hugepages...

If I'm not mistaking, libvirt takes care of the hugepages mount.

A while ago, I've written a wiki to use hugepages in libvirt and Ubuntu. https://help.ubuntu.com/community/KVM%20-%20Using%20Hugepages

Maybe this helps?

________________________________________
Van: G. Richard Bellamy [rbellamy@pteradigm.com]
Verzonden: zaterdag 31 januari 2015 0:33
Aan: libvirt-users@redhat.com
Onderwerp: [libvirt-users] HugePages - can't start guest that requires them

Hello All,

I'm trying to enable hugepages, I've turned off THP (Transparent Huge
Pages), and enabled hugepages in memoryBacking, and set my 2MB
hugepages count via sysctl.

I'm getting "libvirtd[5788]: Failed to autostart VM 'atlas': internal
error: Unable to find any usable hugetlbfs mount for 16777216 KiB"
where atlas is one of my guests and 16777216 KiB is the amount of
memory I'm trying to give to the guest.

Yes, i can see the hugepages via numastat -m and hugetlbfs is mounted
via /dev/hugepages and there is a dir structure
/dev/hugepages/libvirt/qemu (it's empty).

HugePages is big enough to accommodate the 16G i'm allocating... and
changing the perms on that directory structure to 777 doesn't work
either.

Any help is much appreciated.

HOST: http://sprunge.us/SEdc
GUEST: http://sprunge.us/VCYB

Regards,
Richard

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