kern/169480: [zfs] ZFS stalls on heavy I/O

[Harry Coin]

The following reply was made to PR kern/169480; it has been noted by GNATS.

From: Harry Coin <hgcoin at gmail.com>
To: bug-followup at FreeBSD.org, levent.serinol at mynet.com
Cc:  
Subject: Re: kern/169480: [zfs] ZFS stalls on heavy I/O
Date: Fri, 25 Jan 2013 19:26:10 -0600

 I think I have an easier way to reproduce this problem on a very simple 
 setup:
 
 Boot a 'nas4free' livecd version 573 (freebsd 9.1.0.1).   Mount one 
 zpool with no dedup, simple raidz 4 drive setup, 4GB memory.  Don't 
 enable any of the various features, just get a shell from the live cd 
 prompt.  Use dd to make a 20GB file on the pool writing from 
 /dev/random.  While that's going, go to another virtual console cd to 
 the pool, and do an ls -l.   It won't return.  Of interest, long before 
 wired memory explodes to the limit, ls not returning while dd is 
 running, 'top' on another shell reports this:
 
 99.7% idle, 2.6gb free ram, dd in tx->tx, zfskern in zio->i, and intr in 
 WAIT
 
 Eventually disk activity as shown by the cheery little flickering lamp 
 slows, then stops.  Characters still echo on the ls -l command that 
 hasn't returned, but no others.  alt-tab strangely still works. The only 
 way out is to power cycle the box.
 
 Details here:
 
 http://forums.nas4free.org/viewtopic.php?p=12519#p12519
 
 Feels like completed io's are getting lost and the system just waits and 
 waits until there are no more resources left to issue new commands or 
 too many threads are locked waiting for what will never return.
 
 Harry