free_hugepages

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.  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 5.10 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)