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 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)