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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 memory behavior to describe it to
     the system.  The advice passed in may be used by the system to alter its virtual memory paging strat-egy. strategy.
     egy.  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() sys-tem system
                      tem 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 man-ner. manner.
                      ner.  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() system 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() system call.

     MADV_FREE        Indicates that the application will not need the information 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 function is part of IEEE 1003.1-2001
     and was first implemented in Mac OS X 10.2.

BSD                              June 9, 1993                              BSD

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