1.\" $NetBSD: madvise.2,v 1.24 2008/04/22 10:42:16 rmind Exp $ 2.\" 3.\" Copyright (c) 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93 31.\" 32.Dd April 19, 2008 33.Dt MADVISE 2 34.Os 35.Sh NAME 36.Nm madvise 37.Nd give advice about use of memory 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/mman.h 42.Ft int 43.Fn madvise "void *addr" "size_t len" "int behav" 44.Ft int 45.Fn posix_madvise "void *addr" "size_t len" "int advice" 46.Sh DESCRIPTION 47The 48.Fn madvise 49system call 50allows a process that has knowledge of its memory behavior 51to describe it to the system. 52The 53.Fn posix_madvise 54interface is identical and is provided for standards conformance. 55.Pp 56The known behaviors are: 57.Bl -tag -width MADV_NORMAL 58.It Dv MADV_NORMAL 59Tells the system to revert to the default paging 60behavior. 61.It Dv MADV_RANDOM 62Is a hint that pages will be accessed randomly, and prefetching 63is likely not advantageous. 64.It Dv MADV_SEQUENTIAL 65Causes the VM system to depress the priority of 66pages immediately preceding a given page when it is faulted in. 67.It Dv MADV_WILLNEED 68Causes pages that are in a given virtual address range 69to temporarily have higher priority, and if they are in 70memory, decrease the likelihood of them being freed. 71Additionally, 72the pages that are already in memory will be immediately mapped into 73the process, thereby eliminating unnecessary overhead of going through 74the entire process of faulting the pages in. 75This WILL NOT fault 76pages in from backing store, but quickly map the pages already in memory 77into the calling process. 78.It Dv MADV_DONTNEED 79Allows the VM system to decrease the in-memory priority 80of pages in the specified range. 81Additionally future references to 82this address range will incur a page fault. 83.It Dv MADV_FREE 84Gives the VM system the freedom to free pages, 85and tells the system that information in the specified page range 86is no longer important. 87.El 88.Pp 89Portable programs that call the 90.Fn posix_madvise 91interface should use the aliases 92.Dv POSIX_MADV_NORMAL , POSIX_MADV_SEQUENTIAL , 93.Dv POSIX_MADV_RANDOM , POSIX_MADV_WILLNEED , 94and 95.Dv POSIX_MADV_DONTNEED 96rather than the flags described above. 97.Sh RETURN VALUES 98Upon successful completion, 99a value of 0 is returned. 100Otherwise, a value of \-1 is returned and 101.Va errno 102is set to indicate the error. 103.Sh ERRORS 104.Fn madvise 105will fail if: 106.Bl -tag -width Er 107.It Bq Er EINVAL 108Invalid parameters were provided. 109.El 110.Sh SEE ALSO 111.Xr mincore 2 , 112.Xr mprotect 2 , 113.Xr msync 2 , 114.Xr munmap 2 , 115.Xr posix_fadvise 2 116.Sh STANDARDS 117The 118.Fn posix_madvise 119system call is expected to conform to the 120.St -p1003.1-2001 121standard. 122.Sh HISTORY 123The 124.Nm madvise 125system call first appeared in 126.Bx 4.4 , 127but until 128.Nx 1.5 129it did not perform any of the requests on, or change any behavior of the 130address range given. The 131.Fn posix_madvise 132was invented in 133.Nx 5.0 . 134