Huge Page Support: Difference between revisions

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<!-- The following is old and perhaps Oracle-VM-specific:
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* Create the VM with option `superpages = 1`.
* Create the VM with option `superpages = 1`.

Notes:
Notes:


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


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


Revision as of 13:46, 7 May 2015


What Are 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 HVM and PVH guests (use in PV guests is not supported). The hypervisor itself uses huge pages wherever it can.

Using Huge Pages

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

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