HugeTLB on ARM64

[Andreas Schaufler <andreas.schaufler@gmx.de>]

Dear all,

I am working on a project based on a A53 SoC. The goal is for the CPU to
receive and process data. I am running vanilla 5.4.9.

Benchmarking memory performance shows improvements when using HugeTLBs.
I managed to run with 4K base pages and 2MB Huge
Pages specifying on the kernel command line how many pages to allocate,
i.e. hugepages=512 default_hugepagesz=2m hugepagesz=2m.

The ARM64 when using 4K pages should also support 1G Huge Pages.
However, when specifying this:

hugepages=1 default_hugepagesz=1G hugepagesz=1G

I see the size properly taken into account in /proc/meminfo, but it does
not manage to allocate them:

# cat /proc/meminfo
…..
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:    1048576 kB
Hugetlb:               0 kB

There is enough memory on the board. For instance if I declare a CMA
area of 1G in the device tree it manges to reserve it properly at
0x40000000. Of course I remove CMA reservation when defining 1G Huge Pages.

I am looking for the reason why this would fail, but I am not
successful. Any hints will be highly appreciated.

Thanks a lot and best regards
Andreas