571562fffb
First, extend the changes in r230782 to better handle the common case of using NOREUSE with sequential reads. A NOREUSE file descriptor will now track the last implicit DONTNEED request it made as a result of a NOREUSE read. If a subsequent NOREUSE read is adjacent to the previous range, it will apply the DONTNEED request to the entire range of both the previous read and the current read. The effect is that each read of a file accessed sequentially will apply the DONTNEED request to the entire range that has been read. This allows NOREUSE to properly handle misaligned reads by flushing each buffer to cache once it has been completely read. Second, apply the same changes made to read(2) by r230782 and this change to writes. This provides much better performance in the sequential write case as it allows writes to still be clustered. It also provides much better performance for misaligned writes. It does mean that NOREUSE will be generally ineffective for non-sequential writes as the current implementation relies on a future NOREUSE write's implicit DONTNEED request to flush the dirty buffer from the current write. MFC after: 2 weeks
138 lines
4.1 KiB
Groff
138 lines
4.1 KiB
Groff
.\" 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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.\" 4. 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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.\" $FreeBSD$
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.\"
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.Dd June 19, 2012
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.Dt POSIX_FADVISE 2
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.Os
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.Sh NAME
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.Nm posix_fadvise
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.Nd give advice about use of file data
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In fcntl.h
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.Ft int
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.Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice"
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.Sh DESCRIPTION
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The
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.Fn posix_fadvise
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system call
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allows a process to describe to the system its data access behavior for an
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open file descriptor
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.Fa fd .
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The advice covers the data starting at offset
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.Fa offset
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and continuing for
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.Fa len
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bytes.
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If
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.Fa len
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is zero,
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all data from
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.Fa offset
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to the end of the file is covered.
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.Pp
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The behavior is specified by the
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.Fa advice
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parameter and may be one of:
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.Bl -tag -width POSIX_FADV_SEQUENTIAL
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.It Dv POSIX_FADV_NORMAL
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Tells the system to revert to the default data access behavior.
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.It Dv POSIX_FADV_RANDOM
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Is a hint that file data will be accessed randomly,
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and prefetching is likely not advantageous.
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.It Dv POSIX_FADV_SEQUENTIAL
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Tells the system that file data will be accessed sequentially.
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This currently does nothing as the default behavior uses heuristics to
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detect sequential behavior.
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.It Dv POSIX_FADV_WILLNEED
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Tells the system that the specified data will be accessed in the near future.
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The system may initiate an asynchronous read of the data if it is not already
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present in memory.
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.It Dv POSIX_FADV_DONTNEED
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Tells the system that the specified data will not be accessed in the near
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future.
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The system may decrease the in-memory priority of clean data within the
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specified range and future access to this data may require a read operation.
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.It Dv POSIX_FADV_NOREUSE
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Tells the system that the specified data will only be accessed once and
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then not reused.
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The system may decrease the in-memory priority of data once it has been
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read or written.
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Future access to this data may require a read operation.
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.El
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.Sh RETURN VALUES
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.Rv -std posix_fadvise
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.Sh ERRORS
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The
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.Fn posix_fadvise
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system call will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument is not a valid file descriptor.
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.It Bq Er EINVAL
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The
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.Fa advice
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argument is not valid.
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.It Bq Er EINVAL
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The
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.Fa offset
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or
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.Fa len
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arguments are negative,
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or
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.Fa offset
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+
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.Fa len
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is greater than the maximum file size.
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.It Bq Er ENODEV
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The
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.Fa fd
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argument does not refer to a regular file.
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.It Bq Er ESPIPE
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The
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.Fa fd
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argument is associated with a pipe or FIFO.
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.El
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.Sh SEE ALSO
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.Xr madvise 2
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.Sh STANDARDS
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The
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.Fn posix_fadvise
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interface conforms to
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.St -p1003.1-2001 .
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.Sh HISTORY
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The
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.Fn posix_fadvise
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system call first appeared in
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.Fx 10.0 .
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