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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 parameter 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 parameter 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
       parameter of alloc_hugepages() is a hint, that the kernel  may  or  may
       not follow.  Addresses must be properly aligned.

       The  len parameter is the length of the required segment.  It must be a
       multiple of the huge page size.

       The prot parameter specifies the memory protection of the segment.   It
       is one of PROT_READ, PROT_WRITE, PROT_EXEC.

       The  flag  parameter 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 3.01 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/.