d/freebsd-nq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
4524013cd3
freebsd-nq/lib/libc/sys/posix_fadvise.2

138 lines
4.1 KiB
Groff
Raw Normal View History

Add the posix_fadvise(2) system call. It is somewhat similar to madvise(2) except that it operates on a file descriptor instead of a memory region. It is currently only supported on regular files. Just as with madvise(2), the advice given to posix_fadvise(2) can be divided into two types. The first type provide hints about data access patterns and are used in the file read and write routines to modify the I/O flags passed down to VOP_READ() and VOP_WRITE(). These modes are thus filesystem independent. Note that to ease implementation (and since this API is only advisory anyway), only a single non-normal range is allowed per file descriptor. The second type of hints are used to hint to the OS that data will or will not be used. These hints are implemented via a new VOP_ADVISE(). A default implementation is provided which does nothing for the WILLNEED request and attempts to move any clean pages to the cache page queue for the DONTNEED request. This latter case required two other changes. First, a new V_CLEANONLY flag was added to vinvalbuf(). This requests vinvalbuf() to only flush clean buffers for the vnode from the buffer cache and to not remove any backing pages from the vnode. This is used to ensure clean pages are not wired into the buffer cache before attempting to move them to the cache page queue. The second change adds a new vm_object_page_cache() method. This method is somewhat similar to vm_object_page_remove() except that instead of freeing each page in the specified range, it attempts to move clean pages to the cache queue if possible. To preserve the ABI of struct file, the f_cdevpriv pointer is now reused in a union to point to the currently active advice region if one is present for regular files. Reviewed by: jilles, kib, arch@ Approved by: re (kib) MFC after: 1 month
2011-11-04 04:02:50 +00:00
.\" Copyright (c) 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93
.\" $FreeBSD$
.\"
Further refine the implementation of POSIX_FADV_NOREUSE. 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
2012-06-19 18:42:24 +00:00
.Dd June 19, 2012
Add the posix_fadvise(2) system call. It is somewhat similar to madvise(2) except that it operates on a file descriptor instead of a memory region. It is currently only supported on regular files. Just as with madvise(2), the advice given to posix_fadvise(2) can be divided into two types. The first type provide hints about data access patterns and are used in the file read and write routines to modify the I/O flags passed down to VOP_READ() and VOP_WRITE(). These modes are thus filesystem independent. Note that to ease implementation (and since this API is only advisory anyway), only a single non-normal range is allowed per file descriptor. The second type of hints are used to hint to the OS that data will or will not be used. These hints are implemented via a new VOP_ADVISE(). A default implementation is provided which does nothing for the WILLNEED request and attempts to move any clean pages to the cache page queue for the DONTNEED request. This latter case required two other changes. First, a new V_CLEANONLY flag was added to vinvalbuf(). This requests vinvalbuf() to only flush clean buffers for the vnode from the buffer cache and to not remove any backing pages from the vnode. This is used to ensure clean pages are not wired into the buffer cache before attempting to move them to the cache page queue. The second change adds a new vm_object_page_cache() method. This method is somewhat similar to vm_object_page_remove() except that instead of freeing each page in the specified range, it attempts to move clean pages to the cache queue if possible. To preserve the ABI of struct file, the f_cdevpriv pointer is now reused in a union to point to the currently active advice region if one is present for regular files. Reviewed by: jilles, kib, arch@ Approved by: re (kib) MFC after: 1 month
2011-11-04 04:02:50 +00:00
.Dt POSIX_FADVISE 2
.Os
.Sh NAME
.Nm posix_fadvise
.Nd give advice about use of file data
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In fcntl.h
.Ft int
.Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice"
.Sh DESCRIPTION
The
.Fn posix_fadvise
system call
allows a process to describe to the system its data access behavior for an
open file descriptor
.Fa fd .
The advice covers the data starting at offset
.Fa offset
and continuing for
.Fa len
bytes.
If
.Fa len
is zero,
all data from
.Fa offset
to the end of the file is covered.
.Pp
The behavior is specified by the
.Fa advice
parameter and may be one of:
.Bl -tag -width POSIX_FADV_SEQUENTIAL
.It Dv POSIX_FADV_NORMAL
Tells the system to revert to the default data access behavior.
.It Dv POSIX_FADV_RANDOM
Is a hint that file data will be accessed randomly,
and prefetching is likely not advantageous.
.It Dv POSIX_FADV_SEQUENTIAL
Tells the system that file data will be accessed sequentially.
This currently does nothing as the default behavior uses heuristics to
detect sequential behavior.
.It Dv POSIX_FADV_WILLNEED
Tells the system that the specified data will be accessed in the near future.
Fix various typos in manual pages. Submitted by: amdmi3 PR: 165431 MFC after: 1 week
2012-02-25 14:31:25 +00:00
The system may initiate an asynchronous read of the data if it is not already
Add the posix_fadvise(2) system call. It is somewhat similar to madvise(2) except that it operates on a file descriptor instead of a memory region. It is currently only supported on regular files. Just as with madvise(2), the advice given to posix_fadvise(2) can be divided into two types. The first type provide hints about data access patterns and are used in the file read and write routines to modify the I/O flags passed down to VOP_READ() and VOP_WRITE(). These modes are thus filesystem independent. Note that to ease implementation (and since this API is only advisory anyway), only a single non-normal range is allowed per file descriptor. The second type of hints are used to hint to the OS that data will or will not be used. These hints are implemented via a new VOP_ADVISE(). A default implementation is provided which does nothing for the WILLNEED request and attempts to move any clean pages to the cache page queue for the DONTNEED request. This latter case required two other changes. First, a new V_CLEANONLY flag was added to vinvalbuf(). This requests vinvalbuf() to only flush clean buffers for the vnode from the buffer cache and to not remove any backing pages from the vnode. This is used to ensure clean pages are not wired into the buffer cache before attempting to move them to the cache page queue. The second change adds a new vm_object_page_cache() method. This method is somewhat similar to vm_object_page_remove() except that instead of freeing each page in the specified range, it attempts to move clean pages to the cache queue if possible. To preserve the ABI of struct file, the f_cdevpriv pointer is now reused in a union to point to the currently active advice region if one is present for regular files. Reviewed by: jilles, kib, arch@ Approved by: re (kib) MFC after: 1 month
2011-11-04 04:02:50 +00:00
present in memory.
.It Dv POSIX_FADV_DONTNEED
Tells the system that the specified data will not be accessed in the near
future.
The system may decrease the in-memory priority of clean data within the
specified range and future access to this data may require a read operation.
.It Dv POSIX_FADV_NOREUSE
Tells the system that the specified data will only be accessed once and
then not reused.
Further refine the implementation of POSIX_FADV_NOREUSE. 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
2012-06-19 18:42:24 +00:00
The system may decrease the in-memory priority of data once it has been
read or written.
Future access to this data may require a read operation.
Add the posix_fadvise(2) system call. It is somewhat similar to madvise(2) except that it operates on a file descriptor instead of a memory region. It is currently only supported on regular files. Just as with madvise(2), the advice given to posix_fadvise(2) can be divided into two types. The first type provide hints about data access patterns and are used in the file read and write routines to modify the I/O flags passed down to VOP_READ() and VOP_WRITE(). These modes are thus filesystem independent. Note that to ease implementation (and since this API is only advisory anyway), only a single non-normal range is allowed per file descriptor. The second type of hints are used to hint to the OS that data will or will not be used. These hints are implemented via a new VOP_ADVISE(). A default implementation is provided which does nothing for the WILLNEED request and attempts to move any clean pages to the cache page queue for the DONTNEED request. This latter case required two other changes. First, a new V_CLEANONLY flag was added to vinvalbuf(). This requests vinvalbuf() to only flush clean buffers for the vnode from the buffer cache and to not remove any backing pages from the vnode. This is used to ensure clean pages are not wired into the buffer cache before attempting to move them to the cache page queue. The second change adds a new vm_object_page_cache() method. This method is somewhat similar to vm_object_page_remove() except that instead of freeing each page in the specified range, it attempts to move clean pages to the cache queue if possible. To preserve the ABI of struct file, the f_cdevpriv pointer is now reused in a union to point to the currently active advice region if one is present for regular files. Reviewed by: jilles, kib, arch@ Approved by: re (kib) MFC after: 1 month
2011-11-04 04:02:50 +00:00
.El
.Sh RETURN VALUES
.Rv -std posix_fadvise
.Sh ERRORS
The
.Fn posix_fadvise
system call will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument is not a valid file descriptor.
.It Bq Er EINVAL
The
.Fa advice
argument is not valid.
.It Bq Er EINVAL
The
.Fa offset
or
.Fa len
arguments are negative,
or
.Fa offset
+
.Fa len
is greater than the maximum file size.
.It Bq Er ENODEV
The
.Fa fd
argument does not refer to a regular file.
.It Bq Er ESPIPE
The
.Fa fd
argument is associated with a pipe or FIFO.
.El
.Sh SEE ALSO
.Xr madvise 2
.Sh STANDARDS
The
.Fn posix_fadvise
interface conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn posix_fadvise
system call first appeared in
posix_fadvise(2) first appeared in FreeBSD 9.1
2013-01-23 10:50:52 +00:00
.Fx 9.1 .
Reference in New Issue Copy Permalink