GET_HUGEPAGE_REGION(3)					     Library Functions Manual					    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 spec-
       ify 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 allocating a region of memory. 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)