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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, spec-
	      ify this flag.

       GHR_DEFAULT
	      The library chooses a sensible combination of flags for allocating a region of mem-
	      ory. The current default is:	GHR_FALLBACK | 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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