b6cbf7203b
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
133 lines
4.4 KiB
Groff
133 lines
4.4 KiB
Groff
.\" $NetBSD: madvise.2,v 1.26 2009/06/03 09:04:18 wiz Exp $
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.\"
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.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93
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.\"
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.Dd June 2, 2009
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.Dt MADVISE 2
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.Os
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.Sh NAME
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.Nm madvise
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.Nd give advice about use of memory
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/mman.h
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.Ft int
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.Fn madvise "void *addr" "size_t len" "int behav"
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.Ft int
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.Fn posix_madvise "void *addr" "size_t len" "int advice"
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.Sh DESCRIPTION
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The
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.Fn madvise
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system call
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allows a process that has knowledge of its memory behavior
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to describe it to the system.
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The
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.Fn posix_madvise
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interface is identical and is provided for standards conformance.
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.Pp
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The known behaviors are:
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.Bl -tag -width MADV_NORMAL
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.It Dv MADV_NORMAL
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Tells the system to revert to the default paging
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behavior.
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.It Dv MADV_RANDOM
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Is a hint that pages will be accessed randomly, and prefetching
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is likely not advantageous.
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.It Dv MADV_SEQUENTIAL
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Is a hint that pages will be accessed sequentially, from the lower address to
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higher address.
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It might cause the VM system to depress the priority of
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pages immediately preceding a given page when it is faulted in.
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.It Dv MADV_WILLNEED
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Is a hint that pages will be accessed in the near future.
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It might cause the VM system to make pages that are in a given virtual
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address range to temporarily have higher priority, and if they are in
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memory, decrease the likelihood of them being freed.
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It might immediately map the pages that are already in memory into the
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process, thereby eliminating unnecessary overhead of going through
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the entire process of faulting the pages in.
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It might or might not fault pages in from backing store.
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.It Dv MADV_DONTNEED
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Is a hint that pages will not be accessed in the near future.
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It might allow the VM system to decrease the in-memory priority
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of pages in the specified range.
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.It Dv MADV_FREE
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Gives the VM system the freedom to free pages,
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and tells the system that information in the specified page range
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is no longer important.
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.El
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.Pp
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Portable programs that call the
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.Fn posix_madvise
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interface should use the aliases
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.Dv POSIX_MADV_NORMAL , POSIX_MADV_SEQUENTIAL ,
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.Dv POSIX_MADV_RANDOM , POSIX_MADV_WILLNEED ,
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and
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.Dv POSIX_MADV_DONTNEED
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rather than the flags described above.
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.Sh RETURN VALUES
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Upon successful completion,
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a value of 0 is returned.
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Otherwise, a value of \-1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn madvise
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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Invalid parameters were provided.
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.El
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.Sh SEE ALSO
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.Xr mincore 2 ,
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.Xr mprotect 2 ,
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.Xr msync 2 ,
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.Xr munmap 2 ,
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.Xr posix_fadvise 2
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.Sh STANDARDS
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The
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.Fn posix_madvise
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system call is expected to conform to the
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.St -p1003.1-2001
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standard.
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.Sh HISTORY
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The
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.Nm madvise
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system call first appeared in
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.Bx 4.4 ,
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but until
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.Nx 1.5
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it did not perform any of the requests on, or change any behavior of the
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address range given.
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The
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.Fn posix_madvise
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was invented in
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.Nx 5.0 .
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