| madvise.2 (14326) | madvise.2 (17229) |
|---|---|
| 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. --- 17 unchanged lines hidden (view full) --- 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.\" | 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. --- 17 unchanged lines hidden (view full) --- 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.\" |
| 34.Dd June 9, 1993 | 34.Dd Jul 19, 1996 |
| 35.Dt MADVISE 2 36.Os 37.Sh NAME 38.Nm madvise 39.Nd give advise about use of memory 40.Sh SYNOPSIS 41.Fd #include <sys/types.h> 42.Fd #include <sys/mman.h> 43.Fn madvise "caddr_t addr" "size_t len" "int behav" 44.Sh DESCRIPTION 45The 46.Fn madvise 47system call 48allows a process that has knowledge of its memory behavior 49to describe it to the system. 50The known behaviors are given in 51.Pa <sys/mman.h> : 52.Bd -literal | 35.Dt MADVISE 2 36.Os 37.Sh NAME 38.Nm madvise 39.Nd give advise about use of memory 40.Sh SYNOPSIS 41.Fd #include <sys/types.h> 42.Fd #include <sys/mman.h> 43.Fn madvise "caddr_t addr" "size_t len" "int behav" 44.Sh DESCRIPTION 45The 46.Fn madvise 47system call 48allows a process that has knowledge of its memory behavior 49to describe it to the system. 50The known behaviors are given in 51.Pa <sys/mman.h> : 52.Bd -literal |
| 53#define MADV_NORMAL 0 /* no further special treatment */ 54#define MADV_RANDOM 1 /* expect random page references */ 55#define MADV_SEQUENTIAL 2 /* expect sequential references */ 56#define MADV_WILLNEED 3 /* will need these pages */ 57#define MADV_DONTNEED 4 /* don't need these pages */ 58#define MADV_SPACEAVAIL 5 /* insure that resources are reserved */ | 53#define MADV_NORMAL 0 /* no further special treatment */ 54#define MADV_RANDOM 1 /* expect random page references */ 55#define MADV_SEQUENTIAL 2 /* expect sequential references */ 56#define MADV_WILLNEED 3 /* will need these pages */ 57#define MADV_DONTNEED 4 /* don't need these pages */ 58#define MADV_FREE 5 /* data is now unimportant */ |
| 59.Ed | 59.Ed |
| 60.sp 61MADV_NORMAL tells the system to revert to the default paging 62behavior. 63.sp 64MADV_RANDOM is a hint that pages will be accessed randomly, and prefetching 65is likely not advantageous. 66.sp 67MADV_SEQUENTIAL causes the VM system to depress the priority of 68pages immediately preceeding a given page when it is faulted in. 69.sp 70MADV_WILLNEED causes pages that are in a given virtual address range 71to temporarily have higher priority, and if they are in 72memory, decrease the likelihood of them being freed. Additionally, 73the pages that are already in memory will be immediately mapped into 74the process, thereby eliminating unnecessary overhead of going through 75the entire process of faulting the pages in. This WILL NOT fault 76pages in from backing store, but quickly map the pages already in memory 77into the calling process. 78.sp 79MADV_DONTNEED allows the VM system to decrease the in-memory priority 80of pages in the specified range. Additionally future references to 81this address range will incur a page fault. 82.sp 83MADV_FREE gives the VM system the freedom to free pages, 84and and tells the system that information in the specified page range 85is no longer important. This is an efficient way of allowing malloc(3) to 86free pages anywhere in the address space, while keeping the address space 87valid. The next time that the page is referenced, the page might be demand 88zeroed, or might contain the data that was there before the MADV_FREE call. 89References made to that address space range will not make the VM system 90page the information back in from backing store until the page is 91modified again. 92 |
|
| 60.Sh SEE ALSO 61.Xr msync 2 , 62.Xr munmap 2 , 63.Xr mprotect 2 , 64.Xr mincore 2 . 65 | 93.Sh SEE ALSO 94.Xr msync 2 , 95.Xr munmap 2 , 96.Xr mprotect 2 , 97.Xr mincore 2 . 98 |
| 66.Sh BUGS 67.Nm madvise 68is not yet implemented. 69 | |
| 70.Sh HISTORY 71The 72.Nm madvise 73function first appeared in 4.4BSD. | 99.Sh HISTORY 100The 101.Nm madvise 102function first appeared in 4.4BSD. |