• NAME
  
  alloc_hugepages, free_hugepages - allocate or free huge pages
• SYNOPSIS
  

  
   void *alloc_hugepages(int  key , void * addr , size_t  len ,
                          int  prot , int  flag ); 
  
  
  
  
  
  
  
      int free_hugepages(void * addr ); 
  
  
  

• DESCRIPTION
  
  The system calls
  alloc_hugepages ()
  and
  free_hugepages ()
  were introduced in Linux 2.5.36 and removed again in 2.5.54.
  They existed only on i386 and ia64 (when built with
  CONFIG_HUGETLB_PAGE ).
  In Linux 2.4.20 the syscall numbers exist,
  but the calls fail with the error
  ENOSYS .
  
  On i386 the memory management hardware knows about ordinary pages (4 KiB)
  and huge pages (2 or 4 MiB).
  Similarly ia64 knows about huge pages of
  several sizes.
  These system calls serve to map huge pages into the
  process's memory or to free them again.
  Huge pages are locked into memory, and are not swapped.
  
  The
  key
  argument is an identifier.
  When zero the pages are private, and
  not inherited by children.
  When positive the pages are shared with other applications using the same
  key ,
  and inherited by child processes.
  
  The
  addr
  argument of
  free_hugepages ()
  tells which page is being freed: it was the return value of a
  call to
  alloc_hugepages ().
  (The memory is first actually freed when all users have released it.)
  The
  addr
  argument of
  alloc_hugepages ()
  is a hint, that the kernel may or may not follow.
  Addresses must be properly aligned.
  
  The
  len
  argument is the length of the required segment.
  It must be a multiple of the huge page size.
  
  The
  prot
  argument specifies the memory protection of the segment.
  It is one of
  PROT_READ ,
  PROT_WRITE ,
  PROT_EXEC .
  
  The
  flag
  argument is ignored, unless
  key
  is positive.
  In that case, if
  flag
  is
  IPC_CREAT ,
  then a new huge page segment is created when none
  with the given key existed.
  If this flag is not set, then
  ENOENT is returned when no segment with the given key exists.
  
• RETURN VALUE
  
  On success,
  alloc_hugepages ()
  returns the allocated virtual address, and
  free_hugepages ()
  returns zero.
  On error, -1 is returned, and
  errno
  is set appropriately.
  
• ERRORS
  

  ENOSYS

  The system call is not supported on this kernel.
  

• FILES
  
  /proc/sys/vm/nr_hugepages
  Number of configured hugetlb pages.
  This can be read and written.
  
  /proc/meminfo
  Gives info on the number of configured hugetlb pages and on their size
  in the three variables HugePages_Total, HugePages_Free, Hugepagesize.
  
• CONFORMING TO
  
  These calls are specific to Linux on Intel processors, and should not be
  used in programs intended to be portable.
  
• NOTES
  
  These system calls are gone;
  they existed only in Linux 2.5.36 through to 2.5.54.
  Now the hugetlbfs file system can be used instead.
  Memory backed by huge pages (if the CPU supports them) is obtained by
  using
  mmap(2)
  to map files in this virtual file system.
  
  The maximal number of huge pages can be specified using the
  hugepages= boot parameter.
  
  
  
  
  
  
• COLOPHON
  
  This page is part of release 3.19 of the Linux
  man-pages
  project.
  A description of the project,
  and information about reporting bugs,
  can be found at
  http://www.kernel.org/doc/man-pages/.
  

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