Huge Page Support

This page is new and needs review for accuracy and completeness.

Huge Pages

• Huge pages are also known as 'superpages' in FreeBSD (or 'large pages' in the Microsoft Windows world)

• Newer AMD64 processors can use 1GB pages in long mode.

• Linux has supported huge pages on several architectures since the 2.6 series via the hugetlbfs filesystem.

• Xen Project supports allocating huge pages for guest. The hypervisor itself doesn't use huge pages.

Using Huge Pages

• Specify the hypervisor boot command line flag `allowsuperpage` (it was called `allowhugepage` before).

• Create the VM with option `superpages = 1`.

Notes:

1. This option is for PV guest only; it has no effect to HVM guest.
2. With this option, PV guest `memory` and `maxmem` must be 2M aligned. Otherwise the VM cannot be started.

• Specify the Linux boot command line flag `balloon_hugepages`.

• In the guest::

   # echo 20 > /proc/sys/vm/nr_hugepages

   # cat /proc/meminfo
   ...
   AnonHugePages:         0 kB
   HugePages_Total:      20
   HugePages_Free:       20
   HugePages_Rsvd:        0
   HugePages_Surp:        0
   Hugepagesize:       2048 kB
   DirectMap4k:     1056768 kB
   DirectMap2M:           0 kB

References

• Huge Pages: Wikipedia entry for Huge Pages
• Huge Pages: from Linux memory management site
• Huge Page Document: from Kernel.org
• The source document for this page: http://zhigang.org/wiki/XenHugePages