XFS cpu use and slowness

[Thomas Fjellstrom]

I've recently had a couple issues with XFS.

First off I've noticed a few times that XFS becomes VERY slow when its near 
full (a few GB free), even when it's not fragmented. Reads slow down to 
something on the order of 1MB/s, when at full speed I can generally pull 
200MB/s off the raid5 array (its been a long time since I've seen speed 
anywhere near that off of the file system).

And second, I see one or more of the xfsdatad threads using up a significant 
amount of CPU time (30%+) when running a test like: `iozone -s 8G -A` on my 
new 5 disk md raid0 array. Its pretty fast however (570MBs write, 380MB/s 
read). That said, flush-9:0 and kswapd0* also like to use up a lot of cpu at 
the same time (10-30% cpu each)

So it seems xfs is fast when its a fresh file system, but degrades over time 
(I have xfs_fsr set to run automatically every day on my existing xfs fs, I 
can't see it being very fragmented).

* I have no idea why kswapd0 would be using that much cpu, system has 4G ram, 
and most of it is file/disk cache. Doing the tests however seems to push more 
and more into swap. Started out as 0M, during the first test it moved up to 
1MB, and now during a second test its up to 14MB. Not a lot, but more than I 
expected.

-- 
Thomas Fjellstrom
tfjellstrom@xxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/