ALLOC_HUGEPAGES(2)        (2017-09-15)         ALLOC_HUGEPAGES(2)

     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 seg-
          ment is created when none with the given key existed.  If
          this flag is not set, then ENOENT is returned when no seg-
          ment with the given key exists.

     RETURN VALUE
          On success, alloc_hugepages() returns the allocated virtual

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     ALLOC_HUGEPAGES(2)        (2017-09-15)         ALLOC_HUGEPAGES(2)

          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 filesystem 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 filesystem.

          The maximal number of huge pages can be specified using the
          hugepages= boot parameter.

     COLOPHON
          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be
          found at https://www.kernel.org/doc/man-pages/.

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