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order of I/Oorder of I/OPosted Apr 16, 2004 22:53 UTC (Fri) by giraffedata (subscriber, #1954)Parent article: VM changes in 2.6.6 As a result of the changes, the order in which dirty pages are written to disk has changed; writing always happens in file-offset order now. I find that hard to believe. The order in which pages are written to disk is controlled by the block layer/device driver, and tends to be disk address order. I presume this means to say the order in which the I/Os to write dirty pages to disk are requested of the block layer always happens in file-offset order (as opposed to order in which they became dirty) now. It's hard to see how that makes a big difference in performance, considering I/Os to clean all the dirty pages are requested at about the same time.
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order of I/O Posted Apr 17, 2004 0:17 UTC (Sat) by corbet (editor, #1) [Link] Actually, the order is determined by the I/O scheduler. But the scheduler can only work with requests once they are handed to it. Changing that order can make a big difference in what the driver sees. And, apparently, in some situations, the performance difference can be significant - either better or worse.
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