Commit d70d0711edd8076ec2ce0ed109106e2df950681b
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Jens Axboe
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block: Add sysfs documentation for the discard topology parameters
Add documentation for the discard I/O topology parameters exported in sysfs. Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
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Documentation/ABI/testing/sysfs-block
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142 | 142 | with the previous I/O request are enabled. When set to 2, |
143 | 143 | all merge tries are disabled. The default value is 0 - |
144 | 144 | which enables all types of merge tries. |
145 | + | |
146 | +What: /sys/block/<disk>/discard_alignment | |
147 | +Date: May 2011 | |
148 | +Contact: Martin K. Petersen <martin.petersen@oracle.com> | |
149 | +Description: | |
150 | + Devices that support discard functionality may | |
151 | + internally allocate space in units that are bigger than | |
152 | + the exported logical block size. The discard_alignment | |
153 | + parameter indicates how many bytes the beginning of the | |
154 | + device is offset from the internal allocation unit's | |
155 | + natural alignment. | |
156 | + | |
157 | +What: /sys/block/<disk>/<partition>/discard_alignment | |
158 | +Date: May 2011 | |
159 | +Contact: Martin K. Petersen <martin.petersen@oracle.com> | |
160 | +Description: | |
161 | + Devices that support discard functionality may | |
162 | + internally allocate space in units that are bigger than | |
163 | + the exported logical block size. The discard_alignment | |
164 | + parameter indicates how many bytes the beginning of the | |
165 | + partition is offset from the internal allocation unit's | |
166 | + natural alignment. | |
167 | + | |
168 | +What: /sys/block/<disk>/queue/discard_granularity | |
169 | +Date: May 2011 | |
170 | +Contact: Martin K. Petersen <martin.petersen@oracle.com> | |
171 | +Description: | |
172 | + Devices that support discard functionality may | |
173 | + internally allocate space using units that are bigger | |
174 | + than the logical block size. The discard_granularity | |
175 | + parameter indicates the size of the internal allocation | |
176 | + unit in bytes if reported by the device. Otherwise the | |
177 | + discard_granularity will be set to match the device's | |
178 | + physical block size. A discard_granularity of 0 means | |
179 | + that the device does not support discard functionality. | |
180 | + | |
181 | +What: /sys/block/<disk>/queue/discard_max_bytes | |
182 | +Date: May 2011 | |
183 | +Contact: Martin K. Petersen <martin.petersen@oracle.com> | |
184 | +Description: | |
185 | + Devices that support discard functionality may have | |
186 | + internal limits on the number of bytes that can be | |
187 | + trimmed or unmapped in a single operation. Some storage | |
188 | + protocols also have inherent limits on the number of | |
189 | + blocks that can be described in a single command. The | |
190 | + discard_max_bytes parameter is set by the device driver | |
191 | + to the maximum number of bytes that can be discarded in | |
192 | + a single operation. Discard requests issued to the | |
193 | + device must not exceed this limit. A discard_max_bytes | |
194 | + value of 0 means that the device does not support | |
195 | + discard functionality. | |
196 | + | |
197 | +What: /sys/block/<disk>/queue/discard_zeroes_data | |
198 | +Date: May 2011 | |
199 | +Contact: Martin K. Petersen <martin.petersen@oracle.com> | |
200 | +Description: | |
201 | + Devices that support discard functionality may return | |
202 | + stale or random data when a previously discarded block | |
203 | + is read back. This can cause problems if the filesystem | |
204 | + expects discarded blocks to be explicitly cleared. If a | |
205 | + device reports that it deterministically returns zeroes | |
206 | + when a discarded area is read the discard_zeroes_data | |
207 | + parameter will be set to one. Otherwise it will be 0 and | |
208 | + the result of reading a discarded area is undefined. |