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.\"	@(#)madvise.2	8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: December 26 2019 $
.Dt MADVISE 2
.Os
.Sh NAME
.Nm madvise ,
.Nm posix_madvise
.Nd give advice about use of memory
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn madvise "void *addr" "size_t len" "int behav"
.Ft int
.Fn posix_madvise "void *addr" "size_t len" "int behav"
.Sh DESCRIPTION
The
.Fn madvise
system call
allows a process that has knowledge of its memory behavior
to describe it to the system.
The
.Fn posix_madvise
interface has the same effect, but returns the error value
instead of only setting
.Va errno .
.Pp
The possible behaviors are:
.Bl -tag -width MADV_SEQUENTIAL
.It Dv MADV_NORMAL
No further special treatment needed.
.It Dv MADV_RANDOM
Expect random page access patterns.
.It Dv MADV_SEQUENTIAL
Expect sequential page references.
.It Dv MADV_WILLNEED
The pages will be referenced soon.
.It Dv MADV_DONTNEED
The pages will not be referenced soon.
.It Dv MADV_SPACEAVAIL
Ensure that resources are reserved.
.It Dv MADV_FREE
The pages don't contain any useful data and can be recycled.
.El
.Pp
Portable programs that call the
.Fn posix_madvise
interface should use the aliases
.Dv POSIX_MADV_NORMAL , POSIX_MADV_RANDOM ,
.Dv POSIX_MADV_SEQUENTIAL , POSIX_MADV_WILLNEED ,
and
.Dv POSIX_MADV_DONTNEED
rather than the flags described above.
.Sh RETURN VALUES
.Rv -std madvise
.Pp
If successful, the
.Fn posix_madvise
function will return zero.
Otherwise an error number will be returned to indicate the error.
.Sh SEE ALSO
.Xr minherit 2 ,
.Xr mprotect 2 ,
.Xr msync 2 ,
.Xr munmap 2
.Sh STANDARDS
The
.Fn posix_madvise
system call conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn madvise
function first appeared in SunOS 4.0 and has been available since
.Ox 2.7 .
The
.Fn posix_madvise
function first appeared in
.Ox 4.8 .
.Sh BUGS
The
.Dv MADV_WILLNEED
behavior is ignored.
The
.Dv MADV_SPACEAVAIL
behavior is not implemented and will always fail.