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Solving the ext3 latency problem

May 01, 2009, 13:31 (5 Talkback[s])
(Other stories by Jonathan Corbet)

"It's impressive what can happen when attention is drawn to a problem; the 2.6.30 kernel will contain fixes which seemingly eliminate many of the latencies experienced by ext3 users. This article will look at the changes that were made, including a surprising change to the default journaling mode made just before the 2.6.30-rc1 release.

"The problem, in short, is this: the ext3 filesystem, when running in the default data=ordered mode, can exhibit lengthy stalls when some process calls fsync() to flush data to disk. This issue most famously manifested itself as the much-lamented Firefox system-freeze problem, but it goes beyond just Firefox. Anytime there is reasonably heavy I/O going on, an fsync() call can bring everything to a halt for several seconds. Some stalls on the order of minutes have been reported. This behavior has tended to discourage the use of fsync() in applications and it makes the Linux desktop less fun to use. It's clearly worth fixing - but nobody did that for years."

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