| madvise.2 (118684) | madvise.2 (131504) |
|---|---|
| 1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. --- 16 unchanged lines hidden (view full) --- 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93 | 1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. --- 16 unchanged lines hidden (view full) --- 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93 |
| 33.\" $FreeBSD: head/lib/libc/sys/madvise.2 118684 2003-08-09 03:23:24Z bms $ | 33.\" $FreeBSD: head/lib/libc/sys/madvise.2 131504 2004-07-02 23:52:20Z ru $ |
| 34.\" 35.Dd July 19, 1996 36.Dt MADVISE 2 37.Os 38.Sh NAME 39.Nm madvise , posix_madvise 40.Nd give advice about use of memory 41.Sh LIBRARY --- 23 unchanged lines hidden (view full) --- 65Is a hint that pages will be accessed randomly, and prefetching 66is likely not advantageous. 67.It Dv MADV_SEQUENTIAL 68Causes the VM system to depress the priority of 69pages immediately preceding a given page when it is faulted in. 70.It Dv MADV_WILLNEED 71Causes pages that are in a given virtual address range 72to temporarily have higher priority, and if they are in | 34.\" 35.Dd July 19, 1996 36.Dt MADVISE 2 37.Os 38.Sh NAME 39.Nm madvise , posix_madvise 40.Nd give advice about use of memory 41.Sh LIBRARY --- 23 unchanged lines hidden (view full) --- 65Is a hint that pages will be accessed randomly, and prefetching 66is likely not advantageous. 67.It Dv MADV_SEQUENTIAL 68Causes the VM system to depress the priority of 69pages immediately preceding a given page when it is faulted in. 70.It Dv MADV_WILLNEED 71Causes pages that are in a given virtual address range 72to temporarily have higher priority, and if they are in |
| 73memory, decrease the likelihood of them being freed. Additionally, | 73memory, decrease the likelihood of them being freed. 74Additionally, |
| 74the pages that are already in memory will be immediately mapped into 75the process, thereby eliminating unnecessary overhead of going through | 75the pages that are already in memory will be immediately mapped into 76the process, thereby eliminating unnecessary overhead of going through |
| 76the entire process of faulting the pages in. This WILL NOT fault | 77the entire process of faulting the pages in. 78This WILL NOT fault |
| 77pages in from backing store, but quickly map the pages already in memory 78into the calling process. 79.It Dv MADV_DONTNEED 80Allows the VM system to decrease the in-memory priority | 79pages in from backing store, but quickly map the pages already in memory 80into the calling process. 81.It Dv MADV_DONTNEED 82Allows the VM system to decrease the in-memory priority |
| 81of pages in the specified range. Additionally future references to | 83of pages in the specified range. 84Additionally 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 | 85this address range will incur a page fault. 86.It Dv MADV_FREE 87Gives the VM system the freedom to free pages, 88and tells the system that information in the specified page range |
| 86is no longer important. This is an efficient way of allowing | 89is no longer important. 90This is an efficient way of allowing |
| 87.Xr malloc 3 88to free pages anywhere in the address space, while keeping the address space | 91.Xr malloc 3 92to free pages anywhere in the address space, while keeping the address space |
| 89valid. The next time that the page is referenced, the page might be demand | 93valid. 94The next time that the page is referenced, the page might be demand |
| 90zeroed, or might contain the data that was there before the 91.Dv MADV_FREE 92call. 93References made to that address space range will not make the VM system 94page the information back in from backing store until the page is 95modified again. 96.It Dv MADV_NOSYNC 97Request that the system not flush the data associated with this map to | 95zeroed, or might contain the data that was there before the 96.Dv MADV_FREE 97call. 98References made to that address space range will not make the VM system 99page the information back in from backing store until the page is 100modified again. 101.It Dv MADV_NOSYNC 102Request that the system not flush the data associated with this map to |
| 98physical backing store unless it needs to. Typically this prevents the | 103physical backing store unless it needs to. 104Typically this prevents the |
| 99file system update daemon from gratuitously writing pages dirtied | 105file system update daemon from gratuitously writing pages dirtied |
| 100by the VM system to physical disk. Note that VM/file system coherency is | 106by the VM system to physical disk. 107Note that VM/file system coherency is |
| 101always maintained, this feature simply ensures that the mapped data is 102only flush when it needs to be, usually by the system pager. 103.Pp 104This feature is typically used when you want to use a file-backed shared 105memory area to communicate between processes (IPC) and do not particularly 106need the data being stored in that area to be physically written to disk. 107With this feature you get the equivalent performance with mmap that you 108would expect to get with SysV shared memory calls, but in a more controllable | 108always maintained, this feature simply ensures that the mapped data is 109only flush when it needs to be, usually by the system pager. 110.Pp 111This feature is typically used when you want to use a file-backed shared 112memory area to communicate between processes (IPC) and do not particularly 113need the data being stored in that area to be physically written to disk. 114With this feature you get the equivalent performance with mmap that you 115would expect to get with SysV shared memory calls, but in a more controllable |
| 109and less restrictive manner. However, note that this feature is not portable | 116and less restrictive manner. 117However, note that this feature is not portable |
| 110across UNIX platforms (though some may do the right thing by default). 111For more information see the MAP_NOSYNC section of 112.Xr mmap 2 113.It Dv MADV_AUTOSYNC 114Undoes the effects of MADV_NOSYNC for any future pages dirtied within the | 118across UNIX platforms (though some may do the right thing by default). 119For more information see the MAP_NOSYNC section of 120.Xr mmap 2 121.It Dv MADV_AUTOSYNC 122Undoes the effects of MADV_NOSYNC for any future pages dirtied within the |
| 115address range. The effect on pages already dirtied is indeterminate - they 116may or may not be reverted. You can guarantee reversion by using the | 123address range. 124The effect on pages already dirtied is indeterminate - they 125may or may not be reverted. 126You can guarantee reversion by using the |
| 117.Xr msync 2 118or 119.Xr fsync 2 120system calls. 121.It Dv MADV_NOCORE 122Region is not included in a core file. 123.It Dv MADV_CORE 124Include region in a core file. --- 52 unchanged lines hidden --- | 127.Xr msync 2 128or 129.Xr fsync 2 130system calls. 131.It Dv MADV_NOCORE 132Region is not included in a core file. 133.It Dv MADV_CORE 134Include region in a core file. --- 52 unchanged lines hidden --- |