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.