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Date: Tue, 07 Apr 2009 16:03:38 +0200 From: Jos Houtman <jos@...es.nl> To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Wu Fengguang <fengguang.wu@...el.com> Subject: RE: [PATCH 0/7] Per-bdi writeback flusher threads I tried the write-back branch from the 2.6-block tree. And I can atleast confirm that it works, atleast in relation to the writeback not keeping up when the device was congested before it wrote a 1024 pages. See: http://lkml.org/lkml/2009/3/22/83 for a bit more information. But the second problem seen in that thread, a write-starve-read problem does not seem to solved. In this problem the writes of the writeback algorithm starve the ongoing reads, no matter what io-scheduler is picked. For good measure I also applied the blk-latency patches on top of the writeback branch, this did not improve anything. Nor did lowering max_sectors_kb, as linus suggested in the IO latency thread. As for a reproducible test-case: the simplest I could come up with was modifying the fsync-tester not to fsync, but letting the normal writeback handle it. And starting a separate process that tries to sequentially read a file from the same device. The read performance drops to a bare minimum as soon as the writeback algorithm kicks in. Jos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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