1.\" $NetBSD: madvise.2,v 1.29 2017/02/03 21:10:22 abhinav 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 March 29, 2011 33.Dt MADVISE 2 34.Os 35.Sh NAME 36.Nm madvise , 37.Nm posix_madvise 38.Nd give advice about use of memory 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/mman.h 43.Ft int 44.Fn madvise "void *addr" "size_t len" "int behav" 45.Ft int 46.Fn posix_madvise "void *addr" "size_t len" "int advice" 47.Sh DESCRIPTION 48The 49.Fn madvise 50system call 51allows a process that has knowledge of its memory behavior 52to describe it to the system. 53The 54.Fn posix_madvise 55interface is identical and is provided for standards conformance. 56.Pp 57The known behaviors are: 58.Bl -tag -width MADV_SEQUENTIAL 59.It Dv MADV_NORMAL 60Tells the system to revert to the default paging 61behavior. 62.It Dv MADV_RANDOM 63Is a hint that pages will be accessed randomly, and prefetching 64is likely not advantageous. 65.It Dv MADV_SEQUENTIAL 66Is a hint that pages will be accessed sequentially, from the lower address to 67higher address. 68It might cause the VM system to depress the priority of 69pages immediately preceding a given page when it is faulted in. 70.It Dv MADV_WILLNEED 71Is a hint that pages will be accessed in the near future. 72It might cause the VM system to make pages that are in a given virtual 73address range to temporarily have higher priority, and if they are in 74memory, decrease the likelihood of them being freed. 75It might immediately map the pages that are already in memory into the 76process, thereby eliminating unnecessary overhead of going through 77the entire process of faulting the pages in. 78It might or might not fault pages in from backing store. 79.It Dv MADV_DONTNEED 80Is a hint that pages will not be accessed in the near future. 81It might allow the VM system to decrease the in-memory priority 82of pages in the specified range. 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. 131The 132.Fn posix_madvise 133call was added in 134.Nx 5.0 . 135