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 5.05 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/.