[ovirt-users] Question about Huge Pages

[Michal Skrivanek]

> On 18 Apr 2017, at 18:03, Gianluca Cecchi <gianluca.cecchi at gmail.com> wrote:
>
> Hello,
> I'm testing virtualization of some Oracle servers.
> I have 4.1.1 with CentOS 7.3 servers as hypervisors.
> Typically on physical Oracle servers I configure huge pages for Oracle memory areas.
> In particular I disable Transparent Huge Pages, because they are known to be in conflict with Oracle performances, both in RAC and in standalone configurations.
> In RHEL systems I configure "transparent_hugepage=never" boot parameter, while in Oracle Linux OS uek kernels it is already disabled by default.
> I notice that in CentOS 7.3, by default, transparent huge pages are configured:
>
> [root at ov300 ~]# cat /proc/meminfo | grep -i huge
> AnonHugePages:  17006592 kB
> HugePages_Total:       0
> HugePages_Free:        0
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:       2048 kB
> [root at ov300 ~]#
>
> I'm going to configure a VM with 64Gb of ram and with an Oracle RDBMS that would have 16Gb of SGA.
> I suspect that I could have problems if I dont' change configuration at hypervisor level...
>
> What do you think about this subject?
> Is there any drawback if I manually configure the hypervisors to boot with  the "transparent_hugepage=never" boot parameter?

Why not reserving regular hugepages for VMs on boot? then you can use
it with vdsm hook for that Oracle VM. 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.
Also, I suppose you disable KSM, and I'm not sure about ballooning,
unless you need it I'd disable it too.

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

Thanks,
michal
>
> Thanks in advance,
> Gianluca
> _______________________________________________
> Users mailing list
> Users at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/users