Re: Thread model (was: Ext2 superblock fault)

[Thomas Bushnell BSG]

On Sun, 2008-03-16 at 08:52 +0100, olafBuddenhagen@gmx.net wrote:
> Hi,
> 
> On Tue, Mar 11, 2008 at 11:19:32AM +0000, Samuel Thibault wrote:
> > olafBuddenhagen@gmx.net, le Tue 11 Mar 2008 04:53:45 +0100, a écrit :
> 
> > > [I] suggested a more adaptive approach: Keep track of the existing
> > > threads, and if none of them makes progress in a certain amount of
> > > time (say 100 ms), allow creating some more threads. But that was
> > > never implemented. Also, it still might cause considerable delays in
> > > some situations; and I'm not even sure it would fix all problems. (I
> > > didn't fully understand the problem discussed in this thread, so I
> > > don't know whether it would be fixed by that?)
> > 
> > The problem I was observing is when you have a sync_all which triggers
> > the write of a lot of files, but unfortunately the superblock was
> > paged out, so that you aren't able to start another thread to reload
> > it. Whatever the thresholds you choose, with a big enough load you
> > will still have the problem of resisting to creating enough threads
> > for all these request, plus one for the superblock reload request.
> 
> So the problem is that a lot of requests get queued before the first one
> gets very far, so that when the superblock read is finally requested, it
> ends up at the end of a long queue?

No, the problem we are talking about is an outright deadlock.