XFS hang during xfs_fsr run

[Christoph Hellwig]

On Fri, Mar 12, 2010 at 10:45:19AM +0100, Michael Weissenbacher wrote:
> Hi Dave!
>> Hi Michael - have you got any idea what the files are that are
>> hitting this? This failure is implying that the inode is still dirty
>> after syncing all the data. Is something trying to modify it while
>> XFS is trying to map it?
> Yes, as far as i can tell it's always a file that some process is  
> currently modifying. It happens ofter with some file unter /var/log  
> which syslog is currently modifying. I tried setting the "no-defrag"  
> flag via xfs_io's chattr on all log files but that didn't seem to help.  
> It seems that cyrus imapd is triggering this problem far more likely  
> than any other program. Some examples of files where it usually hangs:
> /var/spool/imap/x/user/xxxx/cyrus.cache (lsof -> cyrus)
> /var/imap/db/log.xxxxxxx (lsof -> cyrus)
> /var/log/xxx.log (lsof -> syslog)

So what's interesting is that cyrus uses mmapp access to files, which
might be an indicator that we have problems with excluding fsr on mmaped
files.