On 15 Feb 2019, at 18:17, Vincent Royer <vincent@epicenergy.ca> wrote:

Thanks, I saw that article and it is a hit helpful, but still I don't see how I can tell how many huge pages and of which size my host supports in the first place.  

2M and 1G on x86 

Do all hosts support a certain number, is this calculated by available RAM? 

No, it’s just what linux kernel and hw architecture support

How do I know what size and amount to specify in the kernel command line?

Amount is on you. Hugepages are generally unusable for other normal apps. It’s a matter of flexibility. You need to leave enough available 4k pages for maintenance processes for OS to work. I’d leave few GBs at least...

Or if you plan to use it for just one VM and not for others then just size it according to that VM’s needs

Thanks,

michal

On Fri, Feb 15, 2019, 2:35 AM Martin Sivak <msivak@redhat.com wrote:

Hi,

the hugepages configuration has two aspects - hugepage size and count. You can have multiple sizes at the same time. I am not sure what the recommended configuration is or how to pass it to kernel so others will have to help here (I think 2M and 1G are the usual sizes).

The VM memory configuration is then taken from two places. The custom property tells oVirt which size of hugepages you want to use (in KiB iirc) and the actual number of used hugepages is computed from the total memory configured for the VM at the usual place (it has to be a multiple of the selected hugepage size).

One of our colleagues wrote a blog post about this: https://mpolednik.github.io/2017/06/26/hugepages-and-ovirt/

Best regards

Martin Sivak

On Fri, Feb 15, 2019 at 5:35 AM Vincent Royer <vincent@epicenergy.ca> wrote:

How do I know how many huge pages my hosts can support?

cat /proc/meminfo | grep Huge

 AnonHugePages:  17684480 kB

HugePages_Total:       0

HugePages_Free:        0

HugePages_Rsvd:        0

HugePages_Surp:        0

Hugepagesize:       2048 kB 

And once I know, I set the kernel parameters here, and reboot the host, correct?

And then I assume I assign them to the VM here?  How do I decide how many huge pages and what size a particular VM can benefit from?

<image.png>

Is there a part of the docs I am not finding that covers this?

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