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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 return 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’ memory or to free them again.  Huge pages are locked into mem‐
        ory, 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  pro‐
        cesses.
 
        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 param‐
        eter 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.
        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.
        These calls existed only in Linux  2.5.36  through  to  2.5.54.   These
        calls are specific to Linux on Intel processors, and should not be used
        in programs intended to be portable. Indeed, the  system  call  numbers
        are  marked  for reuse, so programs using these may do something random
        on a future 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.
 

NOTES

        The  system  calls  are  gone. Now the hugetlbfs filesystem can be used
        instead.  Memory backed by huge pages (if the  CPU  supports  them)  is
        obtained by using mmap() to map files in this virtual filesystem.
 
        The  maximal number of huge pages can be specified using the hugepages=
        boot parameter.
 

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