1.\" $NetBSD: madvise.2,v 1.28 2014/07/19 19:26:47 dholland 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.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_SEQUENTIAL 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 65Is a hint that pages will be accessed sequentially, from the lower address to 66higher address. 67It might cause the VM system to depress the priority of 68pages immediately preceding a given page when it is faulted in. 69.It Dv MADV_WILLNEED 70Is a hint that pages will be accessed in the near future. 71It might cause the VM system to make pages that are in a given virtual 72address range to temporarily have higher priority, and if they are in 73memory, decrease the likelihood of them being freed. 74It might immediately map the pages that are already in memory into the 75process, thereby eliminating unnecessary overhead of going through 76the entire process of faulting the pages in. 77It might or might not fault pages in from backing store. 78.It Dv MADV_DONTNEED 79Is a hint that pages will not be accessed in the near future. 80It might allow the VM system to decrease the in-memory priority 81of pages in the specified range. 82.It Dv MADV_FREE 83Gives the VM system the freedom to free pages, 84and tells the system that information in the specified page range 85is no longer important. 86.El 87.Pp 88Portable programs that call the 89.Fn posix_madvise 90interface should use the aliases 91.Dv POSIX_MADV_NORMAL , POSIX_MADV_SEQUENTIAL , 92.Dv POSIX_MADV_RANDOM , POSIX_MADV_WILLNEED , 93and 94.Dv POSIX_MADV_DONTNEED 95rather than the flags described above. 96.Sh RETURN VALUES 97Upon successful completion, 98a value of 0 is returned. 99Otherwise, a value of \-1 is returned and 100.Va errno 101is set to indicate the error. 102.Sh ERRORS 103.Fn madvise 104will fail if: 105.Bl -tag -width Er 106.It Bq Er EINVAL 107Invalid parameters were provided. 108.El 109.Sh SEE ALSO 110.Xr mincore 2 , 111.Xr mprotect 2 , 112.Xr msync 2 , 113.Xr munmap 2 , 114.Xr posix_fadvise 2 115.Sh STANDARDS 116The 117.Fn posix_madvise 118system call is expected to conform to the 119.St -p1003.1-2001 120standard. 121.Sh HISTORY 122The 123.Nm madvise 124system call first appeared in 125.Bx 4.4 , 126but until 127.Nx 1.5 128it did not perform any of the requests on, or change any behavior of the 129address range given. 130The 131.Fn posix_madvise 132call was added in 133.Nx 5.0 . 134