On Wed, Mar 03 2010, John Hughes wrote:
> Jens Axboe wrote:
>> Is IO still going on, or does it appear to be stuck? From the traces
>> below, we have various procs caught in waiting for a request. So if
>> things are totally stuck, it could be some race in there.
>>   
> I see I/O happening on three or four of the disks.
>
> Just a thought.  What exactly is sync(2) supposed to do - block until  
> there are no more dirty pages, or block until all pages that were dirty  
> when the sync was done are clean?  In other words is the problem simply  
> that pages are being dirtied faster than the sync is writing them out?

Our sync is currently broken in that regard, since it'll wait for too
long. We have a debated patch going, I have included it below. Any
chance you could give it a whirl?

The semantics of sync are supposed to be 'wait for dirty IO generated
BEFORE this sync call'.

-- 
Jens Axboe