ALLOC_HUGEPAGES(2)                                  Linux Programmer's Manual                                 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  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 3.25 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/.



Linux                                                      2007-05-31                                         ALLOC_HUGEPAGES(2)