free_hugepages(2) — Linux manual page


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

NAME         top

       alloc_hugepages, free_hugepages - allocate or free huge pages

SYNOPSIS         top

       void *alloc_hugepages(int key, void *addr, size_t len,
                             int prot, int flag);

       int free_hugepages(void *addr);

DESCRIPTION         top

       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

       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         top

       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         top

       ENOSYS The system call is not supported on this kernel.

FILES         top

              Number of configured hugetlb pages.  This can be read and

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

CONFORMING TO         top

       These calls are specific to Linux on Intel processors, and should not
       be used in programs intended to be portable.

NOTES         top

       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         top

       This page is part of release 5.09 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

Linux                            2017-09-15               ALLOC_HUGEPAGES(2)

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