| 1 | '\" t
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| 2 | .\" Title: vfs_readahead
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| 3 | .\" Author: [see the "AUTHOR" section]
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| 4 | .\" Generator: DocBook XSL Stylesheets v1.75.2 <http://docbook.sf.net/>
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| 5 | .\" Date: 10/29/2012
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| 6 | .\" Manual: System Administration tools
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| 7 | .\" Source: Samba 3.6
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| 8 | .\" Language: English
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| 9 | .\"
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| 10 | .TH "VFS_READAHEAD" "8" "10/29/2012" "Samba 3\&.6" "System Administration tools"
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| 11 | .\" -----------------------------------------------------------------
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| 12 | .\" * set default formatting
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| 13 | .\" -----------------------------------------------------------------
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| 14 | .\" disable hyphenation
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| 15 | .nh
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| 16 | .\" disable justification (adjust text to left margin only)
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| 17 | .ad l
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| 18 | .\" -----------------------------------------------------------------
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| 19 | .\" * MAIN CONTENT STARTS HERE *
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| 20 | .\" -----------------------------------------------------------------
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| 21 | .SH "NAME"
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| 22 | vfs_readahead \- pre\-load the kernel buffer cache
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| 23 | .SH "SYNOPSIS"
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| 24 | .HP \w'\ 'u
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| 25 | vfs objects = readahead
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| 26 | .SH "DESCRIPTION"
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| 27 | .PP
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| 28 | This VFS module is part of the
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| 29 | \fBsamba\fR(7)
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| 30 | suite\&.
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| 31 | .PP
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| 32 | This
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| 33 | vfs_readahead
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| 34 | VFS module detects read requests at multiples of a given offset (hex 0x80000 by default) and then tells the kernel via either the readahead system call (on Linux) or the posix_fadvise system call to pre\-fetch this data into the buffer cache\&.
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| 35 | .PP
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| 36 | This module is useful for Windows Vista clients reading data using the Windows Explorer program, which asynchronously does multiple file read requests at offset boundaries of 0x80000 bytes\&.
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| 37 | .PP
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| 38 | The offset multiple used is given by the readahead:offset option, which defaults to 0x80000\&.
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| 39 | .PP
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| 40 | The size of the disk read operations performed by
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| 41 | vfs_readahead
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| 42 | is determined by the readahead:length option\&. By default this is set to the same value as the readahead:offset option and if not set explicitly will use the current value of readahead:offset\&.
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| 43 | .PP
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| 44 | This module is stackable\&.
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| 45 | .SH "OPTIONS"
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| 46 | .PP
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| 47 | readahead:offset = BYTES
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| 48 | .RS 4
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| 49 | The offset multiple that causes readahead to be requested of the kernel buffer cache\&.
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| 50 | .RE
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| 51 | .PP
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| 52 | readahead:length = BYTES
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| 53 | .RS 4
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| 54 | The number of bytes requested to be read into the kernel buffer cache on each readahead call\&.
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| 55 | .RE
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| 56 | .PP
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| 57 | The following suffixes may be applied to BYTES:
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| 58 | .sp
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| 59 | .RS 4
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| 60 | .ie n \{\
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| 61 | \h'-04'\(bu\h'+03'\c
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| 62 | .\}
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| 63 | .el \{\
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| 64 | .sp -1
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| 65 | .IP \(bu 2.3
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| 66 | .\}
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| 67 | K
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| 68 | \- BYTES is a number of kilobytes
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| 69 | .RE
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| 70 | .sp
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| 71 | .RS 4
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| 72 | .ie n \{\
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| 73 | \h'-04'\(bu\h'+03'\c
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| 74 | .\}
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| 75 | .el \{\
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| 76 | .sp -1
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| 77 | .IP \(bu 2.3
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| 78 | .\}
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| 79 | M
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| 80 | \- BYTES is a number of megabytes
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| 81 | .RE
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| 82 | .sp
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| 83 | .RS 4
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| 84 | .ie n \{\
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| 85 | \h'-04'\(bu\h'+03'\c
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| 86 | .\}
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| 87 | .el \{\
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| 88 | .sp -1
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| 89 | .IP \(bu 2.3
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| 90 | .\}
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| 91 | G
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| 92 | \- BYTES is a number of gigabytes
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| 93 | .RE
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| 94 | .SH "EXAMPLES"
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| 95 | .sp
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| 96 | .if n \{\
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| 97 | .RS 4
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| 98 | .\}
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| 99 | .nf
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| 100 | \fI[hypothetical]\fR
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| 101 | \m[blue]\fBvfs objects = readahead\fR\m[]
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| 102 | .fi
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| 103 | .if n \{\
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| 104 | .RE
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| 105 | .\}
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| 106 | .SH "VERSION"
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| 107 | .PP
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| 108 | This man page is correct for version 3\&.0\&.25 of the Samba suite\&.
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| 109 | .SH "AUTHOR"
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| 110 | .PP
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| 111 | The original Samba software and related utilities were created by Andrew Tridgell\&. Samba is now developed by the Samba Team as an Open Source project similar to the way the Linux kernel is developed\&.
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