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= 4k page size vs 64k page size =
|== 4k page size vs 64k page size ==|
Table of Contents
4k page size vs 64k page size
Ubuntu currently supports 4k page size for all architectures except for ppc64el. 64k page sizes are beneficial to certain memory bound benchmarks, but there is a penalty, it might be wasteful if you are dealing with small data structures that have to be page aligned. Also, 64k page size could break compatibility with old ARMv7 binaries. 64k page size will need to reconsidered with the introduction of 52bit VA.
Improve performance benchmarks with 4k pages
There are ways to get comparable performance using 4k page size and avoid the penalties of 64k pages.
- IOMMU Passthrough.
Setting iommu.passthrough to 1 on th kernel command line bypasses the IOMMU translation for DMA, setting it to 0 uses IOMMU translation for DMA. This will need to be set at the time of deployment (using preseeds) or by editing the appropriate grub configuration files and reboot the system for the changes to take effect.
It has been observed that on Cavium Thunder X2 setting the kernel command line parameter iommu.passthrough=1, Flexible I/O Tester Synthetic Benchmark (Fio) performance (with 4k page size) was comparable to that of 64k pages.
This is a runtime feature that can be enabled from userspace, and is currently supported by applications like Java, Qemu and benchmarks like Flexible I/O Tester Synthetic Benchmark (Fio).
Specify the number of hugepages (here I am using 512 as an example, you might need to change that depending on your use case.)
sudo sysctl -w vm.nr_hugepages=512
- Mount the hugetlbfs
sudo mkdir /hugetlbfs sudo mount -t hugetlbfs none /hugetlbfs
Using hugetlbfs with Fio benchmark
With Fio benchmark you can enable mmaphuge for iomem and mem options.
sudo touch hugepages/file sudo fio -rw=read -blocksize=128k -iodepth=128 -buffered=0 -direct=1 -ioengine=libaio -runtime=180 -filename=/dev/nvme0n1 -name=test -time_based -group_reporting -numjobs=4 -iomem=mmaphuge -mem=mmaphuge:/home/ubuntu/hugepages/file -output=output.txt