TU Chemnitz, Fakultät für Informatik, Professur Rechnerarchitektur

Transparent Hugepage Support for Linux

Preliminaries:

Since kernel version 2.6, Linux is able to handle different page sizes concurrently. Thus, beside using 4 KB pages, processes are able to handle so called hugepages with 2 MB, 4 MB or 16 MB size. These pages can be accessed via the HugeTLBfs, which is a pseudo filesystem. Many applications with large amounts of memory (especially HPC applications) can benefit hereof because of the following reasons:

TLB misses may decrease perceptible and
data have a better physical locality in RAM.

To bypass the need for rewriting these applications, a transparent usage is desirable. This can be achieved with help of a preload library that can be linked to applications at start time and overwrites allocation and deallocation functions like malloc(), free(), etc. Our so called "hugepage library" is able to do this and is downloadable below.

System requirements:

Architecture:	x86, x86_64, PPC and PPC64 are supported yet
Kernel version:	2.6, better >= 2.6.16 for MAP_PRIVATE mappings of hugepages
Kernel compile options:	CONFIG_HUGETLBFS=y, CONFIG_HUGETLB_PAGE=y
Compiler:	GCC

Download:

You can download the hugepage library here as free software under a BSD license.

Usage:

Extract and compile the library by issuing

	tar xzf hugepage_library.tar.gz
	cd hugepage_library
	make

After everything compiled cleanly (see the README file for special compile options), you have a 32bit/ subdirectory and a 64bit/ subdirectory for the 64-bit version. There are the following runtime prerequisites:

Hugepages have been allocated (e.g. by "echo 20 > /proc/sys/vm/nr_hugepages")
A HugeTLBfs filesystem has been mounted (e.g. by "mount -t hugetlbfs none /mnt/hugetlb")
Permissions of mounted HugeTLBfs have been set correctly

You can now prove the functionality by preloading the library to a process:

	LD_PRELOAD=32bit/libhugetlbfs.so [command]

References: