MADVISE(2)                  BSD System Calls Manual                 MADVISE(2)

NAME
     madvise, posix_madvise -- give advice about use of memory

SYNOPSIS
     #include <sys/mman.h>

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

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

DESCRIPTION
     The madvise() system call allows a process that has knowledge of its mem-
     ory behavior to describe it to the system.  The advice passed in may be
     used by the system to alter its virtual memory paging strategy.  This
     advice may improve application and system performance.  The behavior
     specified in advice can only be one of the following values:

     MADV_NORMAL      Indicates that the application has no advice to give on
                      its behavior in the specified address range.  This is
                      the system default behavior.  This is used with
                      madvise() system call.

     POSIX_MADV_NORMAL
                      Same as MADV_NORMAL but used with posix_madvise() system
                      call.

     MADV_SEQUENTIAL  Indicates that the application expects to access this
                      address range in a sequential manner.  This is used with
                      madvise() system call.

     POSIX_MADV_SEQUENTIAL
                      Same as MADV_SEQUENTIAL but used with posix_madvise()
                      system call.

     MADV_RANDOM      Indicates that the application expects to access this
                      address range in a random manner.  This is used with
                      madvise() system call.

     POSIX_MADV_RANDOM
                      Same as MADV_RANDOM but used with posix_madvise() system
                      call.

     MADV_WILLNEED    Indicates that the application expects to access this
                      address range soon.  This is used with madvise() system
                      call.

     POSIX_MADV_WILLNEED
                      Same as MADV_WILLNEED but used with posix_madvise() sys-
                      tem call.

     MADV_DONTNEED    Indicates that the application is not expecting to
                      access this address range soon.  This is used with
                      madvise() system call.

     POSIX_MADV_DONTNEED
                      Same as MADV_DONTNEED but used with posix_madvise() sys-
                      tem call.

     MADV_FREE        Indicates that the application will not need the infor-
                      mation contained in this address range, so the pages may
                      be reused right away.  The address range will remain
                      valid.  This is used with madvise() system call.

     MADV_ZERO_WIRED_PAGES
                      Indicates that the application would like the wired
                      pages in this address range to be zeroed out if the
                      address range is deallocated without first unwiring the
                      pages (i.e. a munmap(2) without a preceding munlock(2)
                      or the application quits).  This is used with madvise()
                      system call.

     The posix_madvise() behaves same as madvise() except that it uses values
     with POSIX_ prefix for the advice system call argument.

RETURN VALUES
     Upon successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and errno is set to indicate the error.

ERRORS
     madvise() fails if one or more of the following are true:

     [EINVAL]           The value of advice is incorrect.

     [EINVAL]           The address range includes unallocated regions.

     [ENOMEM]           The virtual address range specified by the addr and
                        len are outside the range allowed for the address
                        space.

LEGACY SYNOPSIS
     #include <sys/types.h>
     #include <sys/mman.h>

     int
     madvise(caddr_t addr, size_t len, int advice);

     int
     posix_madvise(caddr_t addr, size_t len, int advice);

     The include file <sys/types.h> is necessary.  The type of addr has
     changed.

SEE ALSO
     mincore(2), minherit(2), mprotect(2), msync(2), munmap(2), compat(5)

HISTORY
     The madvise function first appeared in 4.4BSD.  The posix_madvise func-
     tion is part of IEEE 1003.1-2001 and was first implemented in Mac OS X
     10.2.

BSD                              June 9, 1993                              BSD