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Using iotop, I found out that [flush-8:0] is doing a lot of hard disk activity, which explains the annoying slowdowns. However, I can't figure out what's the actual cause behind this flushing. No other process seems to be doing inordinate amounts of IO. And you can't strace a kernel task.

I've also enabled IO debugging (via echo 1 >/proc/sys/vm/block_dump), but it gives me block numbers on a JFS filesystem, and I have no idea how to translate those into filenames (just try a web search to see what you get).

I actually have a suspect, a java process that seems to cause hard disk activity whenever I interact with it. But strace -eread,write,open,stat -fp $PID show very little activity. Are there any other syscalls that could cause problems?

Any other ideas?

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I tried the web search to see what I get and got this: wiki.archlinux.org/index.php/Find_File_that_Owns_a_Given_Block –  Wumpus Q. Wumbley Jul 15 '13 at 10:39
    
For some reason I get negative inode numbers using jfs_debugfs (after converting from OS blocks to JFS blocks). In any case this method implies a find -inum, which obviously takes forever. I wonder if there's anything else. –  dan3 Jul 15 '13 at 12:16
    
Attach output of diagnostic utilities to your post, please. –  poige Jul 15 '13 at 13:42

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