POSIX_MADVISE(3P)                                   POSIX Programmer's Manual                                  POSIX_MADVISE(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       posix_madvise - memory advisory information and alignment control (ADVANCED REALTIME)

SYNOPSIS
       #include <sys/mman.h>

       int posix_madvise(void *addr, size_t len, int advice);


DESCRIPTION
       The  posix_madvise()  function  need  only  be  supported  if either the Memory Mapped Files or the Shared Memory Objects
       options are supported.

       The posix_madvise() function shall advise the implementation on the expected behavior of the application with respect  to
       the  data  in the memory starting at address addr, and continuing for len bytes. The implementation may use this informa-
       tion to optimize handling of the specified data. The posix_madvise() function shall have no effect on  the  semantics  of
       access to memory in the specified range, although it may affect the performance of access.

       The  implementation  may  require that addr be a multiple of the page size, which is the value returned by sysconf() when
       the name value _SC_PAGESIZE is used.

       The advice to be applied to the memory range is specified by the advice parameter and may be one of the following values:

       POSIX_MADV_NORMAL

              Specifies that the application has no advice to give on its behavior with respect to the specified  range.  It  is
              the default characteristic if no advice is given for a range of memory.

       POSIX_MADV_SEQUENTIAL

              Specifies  that  the application expects to access the specified range sequentially from lower addresses to higher
              addresses.

       POSIX_MADV_RANDOM

              Specifies that the application expects to access the specified range in a random order.

       POSIX_MADV_WILLNEED

              Specifies that the application expects to access the specified range in the near future.

       POSIX_MADV_DONTNEED

              Specifies that the application expects that it will not access the specified range in the near future.


       These values are defined in the <sys/mman.h> header.

RETURN VALUE
       Upon successful completion, posix_madvise() shall return zero; otherwise, an error number shall be returned  to  indicate
       the error.

ERRORS
       The posix_madvise() function shall fail if:

       EINVAL The value of advice is invalid.

       ENOMEM Addresses  in  the  range starting at addr and continuing for len bytes are partly or completely outside the range
              allowed for the address space of the calling process.


       The posix_madvise() function may fail if:

       EINVAL The value of addr is not a multiple of the value returned by sysconf() when the name value _SC_PAGESIZE is used.

       EINVAL The value of len is zero.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The posix_madvise() function is part of the Advisory Information option and need not be provided on all implementations.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       mmap(), posix_fadvise(), sysconf(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/mman.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy  between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard  is  the  referee   document.   The   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                             POSIX_MADVISE(3P)