free_hugepage_region man page on Oracle

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GET_HUGEPAGE_REGION(3)					GET_HUGEPAGE_REGION(3)

NAME
       get_hugepage_region,  free_hugepage_region  - Allocate and free regions
       of memory that use hugepages where possible

SYNOPSIS
       #include <hugetlbfs.h>

       void *get_hugepage_region(size_t len, ghr_t flags);
       void free_hugepage_region(void *ptr);

DESCRIPTION
       get_hugepage_region() allocates a  memory  region  len  bytes  in  size
       backed  by  hugepages. Hugepages may be of benefit to applications that
       use large amounts of address space and suffer a performance hit due  to
       TLB  misses.  Wall-clock	 time  or oprofile can be used to determine if
       there is a performance benefit from using hugepages or not.

       Unlike get_huge_pages(), len  does  not	have  to  be  hugepage-aligned
       although	 memory	 may  be  wasted due to alignment. The caller may also
       specify that base pages be used in the event  there  are	 no  hugepages
       available.

       The  flags argument changes the behaviour of the function. Flags may be
       or'd together.

       GHR_FALLBACK
	      Use base pages if there  are  an	insufficient  number  of  huge
	      pages.

       GHR_STRICT
	      Use hugepages or return NULL.

       GHR_COLOR
	      When  specified, bytes that would be wasted due to alignment are
	      used to color the buffer by offsetting it by a random  cacheline
	      within  the hugepage.  This avoids a performance problem whereby
	      multiple buffers use the same cache lines at the	same  offsets.
	      If  it  is  not  important that the start of the buffer be page-
	      aligned, specify this flag.

       GHR_DEFAULT
	      The library chooses a sensible combination of flags for allocat‐
	      ing  a  region of memory. The current default is:	     GHR_FALL‐
	      BACK | GHR_COLOR

       free_hugepage_region()  frees  a	 region	  of   memory	allocated   by
       get_hugepage_region(). The behaviour of the function if another pointer
       is used, valid or otherwise, is undefined.

RETURN VALUE
       On success, a pointer is returned  for  to  the	allocated  memory.  On
       error, NULL is returned. errno will be set based on what the failure of
       mmap() was due to.

SEE ALSO
       oprofile(1) , gethugepagesize(3) , get_huge_pages(3) , libhugetlbfs(7)

AUTHORS
       libhugetlbfs was written by various people  on  the  libhugetlbfs-devel
       mailing list.

			       November 7, 2008		GET_HUGEPAGE_REGION(3)
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