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



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

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 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 information 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 POSIX.1-2017, <sys_mman.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                     POSIX_MADVISE(3)
