PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult 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 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.1‐2008, <sys_mman.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .