On Wed, Apr 19, 2017 at 8:03 AM, Michal Skrivanek <mskrivan@redhat.com> wrote:

Why not reserving regular hugepages for VMs on boot?

Do you mean at hypervisor level? In this case it is what I'm doing normally for physical servers where I install Oracle RDBMS

then you can use
it with vdsm hook for that Oracle VM.

Which hook are you referring?

This one:

http://www.ovirt.org/develop/developer-guide/vdsm/hook/hugepages/

In case is it still current? In the sense that I need to mount the hugetblfs virtual file system at hst level?

The hook description seems low detailed...

Normally if I want oracle user able to use huge pages on physical server, I have to specify

# Huge pages

vm.hugetlb_shm_group = 2000

# 18GB allocatable

vm.nr_hugepages = 9216

where 2000 is the group id for dba group, the main group of oracle user

How to map this with vrtualization?

Eg:

1) vm.hugetlb_shm_group at hypervisor side should be set to the group of the qemu user as the qemu-kvm process runs with it?

2) Then I have to set VM for VM the hugepages=xxx value in the hook and that will bypass the sysctl.conf configuration in the guest?

3) I presume I have to set the vm.hugetlb_shm_group parameter at guest level....

Thanks,

Gianluca

It improves VM performance in
general, the only drawback is less flexibility since that memory can't
be used by others unless they specifically ask for hugepages.

This seems to confirm that I have to set a statich sysctl.conf entry at hypervisor level such as

vm.nr_hugepages = YYYY

Also, I suppose you disable KSM, and I'm not sure about ballooning,
unless you need it I'd disable it too.

I kept the defaults at the moment that I suppose should be

a) KSM disabled

ksm has been configured to start by default as normally, but ksmtuned has been disabled:

[g.cecchi@ov300 ~]$ sudo systemctl status ksm

● ksm.service - Kernel Samepage Merging

Loaded: loaded (/usr/lib/systemd/system/ksm.service; enabled; vendor preset: enabled)

Active: active (exited) since Tue 2017-04-11 11:07:28 CEST; 1 weeks 1 days ago

Process: 976 ExecStart=/usr/libexec/ksmctl start (code=exited, status=0/SUCCESS)

Main PID: 976 (code=exited, status=0/SUCCESS)

CGroup: /system.slice/ksm.service

Apr 11 11:07:28 ov300.datacenter.polimi.it systemd[1]: Starting Kernel Samepage Merging...

Apr 11 11:07:28 ov300.datacenter.polimi.it systemd[1]: Started Kernel Samepage Merging.

[g.cecchi@ov300 ~]$ sudo systemctl status ksmtuned

● ksmtuned.service - Kernel Samepage Merging (KSM) Tuning Daemon

Loaded: loaded (/usr/lib/systemd/system/ksmtuned.service; disabled; vendor preset: disabled)

Active: inactive (dead)

[g.cecchi@ov300 ~]$

b) ballooning enabled for a newly created VM unless I explicitly disable it (at least I see this happens in 4.1.1)

What to do for a) and b) to not interfere with huge pages?

The hook is being improved right now in master, but it should be
usable in stable too.

I will be happy to test and verify and contribute to its description, as soon as I understand its usage....

Gianluca