| 1 | .\" Title: vfs_readahead
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| 2 | .\" Author: [see the "AUTHOR" section]
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| 3 | .\" Generator: DocBook XSL Stylesheets v1.74.0 <http://docbook.sf.net/>
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| 4 | .\" Date: 01/27/2009
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| 5 | .\" Manual: System Administration tools
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| 6 | .\" Source: Samba 3.3
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| 7 | .\" Language: English
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| 8 | .\"
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| 9 | .TH "VFS_READAHEAD" "8" "01/27/2009" "Samba 3\&.3" "System Administration tools"
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| 10 | .\" -----------------------------------------------------------------
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| 11 | .\" * (re)Define some macros
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| 68 | .\}
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| 78 | .fi
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| 79 | .in \\n[IN]u
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| 117 | .ie "\\$2"adjust-for-leading-newline" \{\
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| 118 | \M[\\$1]\h'1n'\v'+.5v'\D'P \\n(BWu 0 0 \\n(BHu -\\n(BWu 0 0 -\\n(BHu'\M[]
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| 119 | .\}
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| 121 | \M[\\$1]\h'1n'\v'-.5v'\D'P \\n(BWu 0 0 \\n(BHu -\\n(BWu 0 0 -\\n(BHu'\M[]
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| 122 | .\}
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| 151 | \M[\\$1]\D'P -.75n 0 0 \\n(BHu -(\\n[.i]u - \\n(INu - .75n) 0 0 -\\n(BHu'\M[]
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| 152 | .in 0
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| 157 | .\}
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| 158 | ..
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| 159 | .\" -----------------------------------------------------------------
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| 160 | .\" * set default formatting
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| 161 | .\" -----------------------------------------------------------------
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| 162 | .\" disable hyphenation
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| 163 | .nh
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| 164 | .\" disable justification (adjust text to left margin only)
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| 165 | .ad l
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| 166 | .\" -----------------------------------------------------------------
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| 167 | .\" * MAIN CONTENT STARTS HERE *
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| 168 | .\" -----------------------------------------------------------------
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| 169 | .SH "Name"
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| 170 | vfs_readahead \- pre\-load the kernel buffer cache
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| 171 | .SH "Synopsis"
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| 172 | .fam C
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| 173 | .HP \w'\ 'u
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| 174 | \FCvfs objects = readahead\F[]
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| 175 | .fam
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| 176 | .SH "DESCRIPTION"
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| 177 | .PP
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| 178 | This VFS module is part of the
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| 179 | \fBsamba\fR(7)
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| 180 | suite\&.
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| 181 | .PP
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| 182 | This
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| 183 | \FCvfs_readahead\F[]
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| 184 | 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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| 185 | .PP
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| 186 | 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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| 187 | .PP
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| 188 | The offset multiple used is given by the readahead:offset option, which defaults to 0x80000\&.
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| 189 | .PP
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| 190 | The size of the disk read operations performed by
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| 191 | \FCvfs_readahead\F[]
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| 192 | 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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| 193 | .PP
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| 194 | This module is stackable\&.
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| 195 | .SH "OPTIONS"
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| 196 | .PP
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| 197 | readahead:offset = BYTES
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| 198 | .RS 4
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| 199 | The offset multiple that causes readahead to be requested of the kernel buffer cache\&.
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| 200 | .RE
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| 201 | .PP
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| 202 | readahead:length = BYTES
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| 203 | .RS 4
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| 204 | The number of bytes requested to be read into the kernel buffer cache on each readahead call\&.
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| 205 | .RE
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| 206 | .PP
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| 207 | The following suffixes may be applied to BYTES:
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| 208 | .sp
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| 209 | .RS 4
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| 210 | .ie n \{\
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| 211 | \h'-04'\(bu\h'+03'\c
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| 212 | .\}
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| 213 | .el \{\
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| 214 | .sp -1
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| 215 | .IP \(bu 2.3
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| 216 | .\}
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| 217 | \FCK\F[]
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| 218 | \- BYTES is a number of kilobytes
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| 219 | .RE
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| 220 | .sp
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| 221 | .RS 4
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| 222 | .ie n \{\
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| 223 | \h'-04'\(bu\h'+03'\c
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| 224 | .\}
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| 225 | .el \{\
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| 226 | .sp -1
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| 227 | .IP \(bu 2.3
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| 228 | .\}
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| 229 | \FCM\F[]
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| 230 | \- BYTES is a number of megabytes
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| 231 | .RE
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| 232 | .sp
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| 233 | .RS 4
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| 234 | .ie n \{\
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| 235 | \h'-04'\(bu\h'+03'\c
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| 236 | .\}
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| 237 | .el \{\
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| 238 | .sp -1
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| 239 | .IP \(bu 2.3
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| 240 | .\}
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| 241 | \FCG\F[]
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| 242 | \- BYTES is a number of gigabytes
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| 243 | .SH "EXAMPLES"
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| 244 | .sp
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| 245 | .if n \{\
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| 246 | .RS 4
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| 247 | .\}
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| 248 | .fam C
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| 249 | .ps -1
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| 250 | .nf
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| 251 | .if t \{\
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| 252 | .sp -1
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| 253 | .\}
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| 254 | .BB lightgray adjust-for-leading-newline
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| 255 | .sp -1
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| 256 |
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| 257 | \fI[hypothetical]\fR
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| 258 | \m[blue]\fBvfs objects = readahead\fR\m[]
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| 259 | .EB lightgray adjust-for-leading-newline
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| 260 | .if t \{\
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| 261 | .sp 1
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| 262 | .\}
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| 263 | .fi
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| 264 | .fam
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| 265 | .ps +1
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| 266 | .if n \{\
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| 267 | .RE
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| 268 | .\}
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| 269 | .SH "VERSION"
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| 270 | .PP
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| 271 | This man page is correct for version 3\&.0\&.25 of the Samba suite\&.
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| 272 | .SH "AUTHOR"
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| 273 | .PP
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| 274 | 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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