alloc_hugepages(2)                                      System Calls Manual                                      alloc_hugepages(2)

       alloc_hugepages, free_hugepages - allocate or free huge pages

       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).

       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  al‐
       loc_hugepages().   (The  memory  is  first  actually  freed  when  all  users  have  released it.)  The addr argument of al‐
       loc_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.

       On success, alloc_hugepages() returns the allocated virtual address, and free_hugepages() returns zero.  On error, -1 is re‐
       turned, and errno is set to indicate the error.

       ENOSYS The system call is not supported on this kernel.

              Number of configured hugetlb pages.  This can be read and written.

              Gives  info  on  the  number  of  configured  hugetlb pages and on their size in the three variables HugePages_Total,
              HugePages_Free, Hugepagesize.

       These extinct system calls were specific to Linux on Intel processors.

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

       The maximal number of huge pages can be specified using the hugepages= boot parameter.

Linux man-pages 6.03                                         2022-12-04                                          alloc_hugepages(2)