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== Tools ==
 * libhugetlbfs is a library which provides easy access to huge pages of memory. The library also comes with several userspace tools to help with huge page usability, environment setup, and control. ~-<<BR>>http://libhugetlbfs.ozlabs.org/ <<BR>> DebianBug:533708 - ITP: libhugetlbfs -- Initial package request -~
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Java ; No ; Yes
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 * Get a performance boost by backing your KVM guest with hugetlbfs ~-<<BR>>[[http://www.linux-kvm.com/content/get-performance-boost-backing-your-kvm-guest-hugetlbfs]] (not tested)-~
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=== Java (Sun, OpenJDK) ===
Sun and OpenJDK can use large pages.
 * DebianPkg:sun-java6-bin - Sun Java(TM) Runtime Environment (JRE) 6 (architecture dependent files)
 * DebianPkg:openjdk-6-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless)
http://java.sun.com/javase/technologies/hotspot/largememory.jsp


__Possible errors:__
 * Insufficient {{{/proc/sys/kernel/shmmax}}} ?
 * Not in group defined in {{{/proc/sys/vm/hugetlb_shm_group}}}

 {{{#!text
% java -XX:+UseLargePages
Java HotSpot(TM) Server VM warning: Failed to reserve shared memory (errno = 1).
Java HotSpot(TM) Server VM warning: Failed to reserve shared memory (errno = 22).
}}}
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 * Get a performance boost by backing your KVM guest with hugetlbfs ~-<<BR>>[[http://www.linux-kvm.com/content/get-performance-boost-backing-your-kvm-guest-hugetlbfs]] (note tested)-~  * Article about Huge pages, on LWN.net ~-<<BR>>[[http://lwn.net/Articles/374424/|Introduction]] - [[http://lwn.net/Articles/375096/|Interfaces]] - [[http://lwn.net/Articles/376606/|Administration]] - [[http://lwn.net/Articles/378641/|Benchmarking]]-~

Translation(s): none


Linux "Huge page tables" (HugeTlbPage) is available in Debian since DebianLenny (actually, since 2.6.23).

Currently, there is no standard way to enable HugeTLBfs, mainly because the FHS has no provision for such kind of virtual file system, see 572733 . (Fedora mounts it in /dev/hugepages/, so don't be surprised if you find some example on the web that use this location)

Read the documentation for more information about hugetlbpage.

Enabling HugeTlbPage

  1. Create a group for users of hugepages, and retrieve it's GID (is this example, 2021) then add yourself to the group.
    Note: this should not be needed for libvirt (see /etc/libvirt/qemu.conf)

    % groupadd my-hugetlbfs
    
    % getent group my-hugetlbfs
    my-hugetlbfs:x:2021:
    
    % adduser franklin my-hugetlbfs
    Adding user `franklin' to group `my-hugetlbfs' ...
    Adding user franklin to group my-hugetlbfs
    Done.
  2. Edit /etc/sysctl.conf and add this text to specify the number of page you want to reserve (the HugePages are 4MiB on x86_32, 2MiB on x86_64 and x86_32 PAE)

    # Allocate 256*2MiB for HugePageTables (YMMV)
    vm.nr_hugepages = 256
    
    # Members of group my-hugetlbfs(2021) are allowed to use 
    vm.hugetlb_shm_group = 2021
  3. Create a mount point for the file system

    % mkdir /hugepages
  4. Add this line in /etc/fstab (The mode of 1770 allows anyone in the group to create files but not unlink or rename each other's files.1)

    hugetlbfs /hugepages hugetlbfs mode=1770,gid=2021 0 0
  5. Reboot 2

Getting informations

Well, typically you can retrieve the current available/used page from /proc/meminfo:

  • % grep Huge /proc/meminfo 
    HugePages_Total:     256
    HugePages_Free:      256
    HugePages_Rsvd:        0
    HugePages_Surp:        0
    Hugepagesize:       4096 kB

(read Documentation/vm/hugetlbpage.txt for more information about it)

Standard Debian Kernel have HUGETLB enabled:

  • % grep HUGETLB /boot/config-$(uname -r)
    CONFIG_HUGETLBFS=y
    CONFIG_HUGETLB_PAGE=y

Various runtime settings (see documentation)

  • % grep -R ""  /sys/kernel/mm/hugepages/ /proc/sys/vm/*huge*
    /sys/kernel/mm/hugepages/hugepages-4096kB/nr_hugepages:256
    /sys/kernel/mm/hugepages/hugepages-4096kB/nr_overcommit_hugepages:0
    /sys/kernel/mm/hugepages/hugepages-4096kB/free_hugepages:256
    /sys/kernel/mm/hugepages/hugepages-4096kB/resv_hugepages:0
    /sys/kernel/mm/hugepages/hugepages-4096kB/surplus_hugepages:0
    /proc/sys/vm/hugepages_treat_as_movable:0
    /proc/sys/vm/hugetlb_shm_group:0
    /proc/sys/vm/nr_hugepages:256
    /proc/sys/vm/nr_overcommit_hugepages:0

Tools

  • libhugetlbfs is a library which provides easy access to huge pages of memory. The library also comes with several userspace tools to help with huge page usability, environment setup, and control.
    http://libhugetlbfs.ozlabs.org/
    533708 - ITP: libhugetlbfs -- Initial package request

Hugepage enabled applications

An application can allocate/use HugeTlbPage through two different means:

  1. mmap system call require a mounted hugetlbfs, with appropriate permissions.

  2. Shared memory segment (shmat/shmget system calls or mmap with MAP_HUGETLB), must be member of a group, configured in /proc/sys/vm/hugetlb_shm_group.

    Application hugetlbfs shared memory
    QEMU/KVM No Yes
    MySQM Yes No
    Java No Yes

KVM

MySQL

Linux HugeTLBfs: Improve MySQL Database Application Performance
http://www.cyberciti.biz/tips/linux-hugetlbfs-and-mysql-performance.html (note tested)

Java (Sun, OpenJDK)

Sun and OpenJDK can use large pages.

http://java.sun.com/javase/technologies/hotspot/largememory.jsp

Possible errors:

  • Insufficient /proc/sys/kernel/shmmax ?

  • Not in group defined in /proc/sys/vm/hugetlb_shm_group

    % java -XX:+UseLargePages 
    Java HotSpot(TM) Server VM warning: Failed to reserve shared memory (errno = 1).
    Java HotSpot(TM) Server VM warning: Failed to reserve shared memory (errno = 22).

Documentation

See also


  1. Credits: Russell Coker (1)

  2. This is the most reliable method of allocating huge pages as memory has not yet become fragmented. Yes, you finally found an operation that actually recommend a reboot in Linux ;) (2)