ALLOC_HUGEPAGES(2)                                           Linux Programmer's Manual                                          ALLOC_HUGEPAGES(2)

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.   Mem-
       ory 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/.

Linux                                                               2017-09-15                                                  ALLOC_HUGEPAGES(2)