Messages in this thread | | | Subject | Re: Increase dirty_ratio and dirty_background_ratio? | From | Chris Mason <> | Date | Fri, 09 Jan 2009 14:07:22 -0500 |
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On Fri, 2009-01-09 at 19:02 +0100, Jan Kara wrote:
> What we observe in the seekwatcher graphs is, that there are three > processes writing back the single database file in parallel (2 pdflush > threads because the machine has 2 CPUs, and the database process itself > because of dirty throttling). Each of the processes is writing back the > file at a different offset and so they together create even more random IO > (I'm attaching the graph and can provide blocktrace data if someone is > interested). If there was just one process doing the writeback, we'd be > writing back those data considerably faster...
I spent some time trying similar things for btrfs, and went as far as making my own writeback thread and changing pdflush and throttled writes to wait on it. It was a great hack, but in the end I found the real problem was the way write_cache_pages is advancing the page_index.
You probably remember the related ext4 discussion, and you could try my simple patch in this workload to see if it helps ext3.
http://lkml.org/lkml/2008/10/1/278
Ext3 may need similar tricks.
-chris
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