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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).  Simi-
       larly ia64 knows about huge pages of several sizes.  These system calls serve to map huge pages into  the  pro-
       cess'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 posi-
       tive 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  sys-
       tem  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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2007-05-31                ALLOC_HUGEPAGES(2)