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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  pro-
     cesses.

     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 argu-
     ment 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  writ-
            ten.

     /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 4.16 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)