[dpdk-users] No free hugepages reported in hugepages when running DPDK helloworld example

[James Bensley]

On 23 December 2017 at 21:44, gyp sud <gypsud at gmail.com> wrote:
> I downloaded and built dpdk-stable-16.11.4 version (using
> x86_64-native-linuxapp-gcc target).  I'm running Ubuntu 16.04.3 LTS.
> After setting up hugepages according to http://dpdk.org/doc/quick-start or
> http://dpdk.org/doc/guides-16.04/linux_gsg/sys_reqs.html
>
> mkdir -p /mnt/huge
> mount -t hugetlbfs nodev /mnt/huge
> echo 64 >
> /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
>
> I can see the hugepages fine.
>
> #cat /proc/meminfo | grep
> HugeAnonHugePages:    284672 kB
> ShmemHugePages:        0 kB
> HugePages_Total:      64
> HugePages_Free:       64
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:       2048 kB
>
> But when I run the helloWorld example, it complained about no free
> hugepages, see below.
>
> #./build/helloworld -l 0-3 -n 2
> EAL: Detected 4 lcore(s)
> EAL: No free hugepages reported in hugepages-1048576kB
> EAL: Probing VFIO support...
> hello from core 1
> hello from core 2
> hello from core 3
> hello from core 0
>
> Also, the memory info showed free hugepages were all gone.
> #cat /proc/meminfo | grep Huge
> AnonHugePages:    380928 kB
> ShmemHugePages:        0 kB
> HugePages_Total:      64
> HugePages_Free:        0
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:       2048 kB
>
> Any idea why this is happening?
>
> Gyp

Note the size of the HugePages in the EAL output
"hugepages-1048576kB", you allocated 2MB HugePages, this message is
about 1G HugePages.

1GB HugePages can only be allocated at boot up. It's "OK" though, 1GB
HugePages aren't required, as you saw the application used the 2GB
HugePages you allocated. For some applications and workloads that
require lots of memory fewer 1GB pages can have a performance increase
over more smaller 2MB HugePages.

Obviously it goes without saying it's usually best to install the most
recent DPDK version and check the most recent documentation URL, here
you will find info about setting up 1GB HugePages if you want to do
that:
dpdk.org/doc/guides/linux_gsg/sys_reqs.html

Cheers,
James.