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).  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 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 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.

COLOPHON

       This  page  is  part of release 4.15 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.