[ovs-dev] Hugepages allocation

Bodireddy, Bhanuprakash bhanuprakash.bodireddy at intel.com
Mon Oct 3 12:11:48 UTC 2016

>-----Original Message-----
>From: dev [mailto:dev-bounces at openvswitch.org] On Behalf Of Kapil
>Sent: Monday, October 3, 2016 12:07 PM
>To: dev at openvswitch.org; discuss at openvswitch.org
>Subject: [ovs-dev] Hugepages allocation
>1. in INSTALL.DPDK.md, huge page size is recommended as 2MB pages. Earlier
>i remember seeing some reference to use 1GB huge pages. is there any
>noticeable performance improvement in using 1G hugepages vs 2M pages ?

We did some benchmarks and found that there isn't any significant performance difference using 2MB hugepages over 1GB pages.

>2. is there a way to allocate 1G hugepages using sysctl. Default hugepage size
>is 2M and i didn't find any way to modify it using sysctl. is grub config the only
>way to allocate 1GB pages ?

Yes, for this one has to build kernel with CONFIG_CMA. In case the kernel is built with this, one can allocate hugepages at run time as below
echo N > /sys/devices/system/node/nodeX/hugepages/hugepages-1048576kB/nr_hugepages

>3. Is there any difference in allocating huge pages run time vs
>persistent(/etc/sysctl.d/hugepages.conf) ? will the hugepages allocated at
>runtime will be fragmented or something?
The only advantage of allocating hugepages at boot time is you are sure to get the requested pages as the memory isn't fragmented.
if memory is too fragmented the chances are that  fewer pages would be allocated by kernel than requested.

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