NAME

       alloc_hugepages, free_hugepages - allocate or free huge pages

SYNOPSIS

       void *syscall(SYS_alloc_hugepages, int key, void addr[.len], size_t len,
                     int prot, int flag);
       int syscall(SYS_free_hugepages, void *addr);

       Note: glibc provides no wrappers for these system calls, necessitating the use of syscall(2).

DESCRIPTION

       The system calls alloc_hugepages() and free_hugepages() were introduced in Linux 2.5.36 and removed again
       in Linux 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 to indicate the error.

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.

STANDARDS

       Linux on Intel processors.

HISTORY

       These system calls are gone; they existed only in Linux 2.5.36 through to Linux 2.5.54.

NOTES

       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.