Re: Avoiding the dentry d_lock on final dput(), part deux: transactional memory

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Oct 01, 2013 at 02:52:28PM +1000, Michael Neuling wrote:
> >> Well we don't have to, I think Mikey wasn't totally clear about that
> >> "making all registers volatile" business :-) This is just something we
> >> need to handle in assembly if we are going to reclaim the suspended
> >> transaction.
> 
> Yeah, sorry.  The slow path with all registers as volatile is only
> needed if we get pre-empted during the transaction.
> 
> >>
> >> So basically, what we need is something along the lines of
> >> enable_kernel_tm() which checks if there's a suspended user transaction
> >> and if yes, kills/reclaims it.
> >>
> >> Then we also need to handle in our interrupt handlers that we have an
> >> active/suspended transaction from a kernel state, which we don't deal
> >> with at this point, and do whatever has to be done to kill it... we
> >> might get away with something simple if we can state that we only allow
> >> kernel transactions at task level and not from interrupt/softirq
> >> contexts, at least initially.
> >
> > Call me a coward, but this is starting to sound a bit scary.  ;-)
> 
> We are just wanting to prototype it for now to see if we could make it
> go faster.  If it's worth it, then we'd consider the additional
> complexity this would bring.
> 
> I don't think it'll be that bad, but I'd certainly want to make sure
> it's worth it before trying :-)

OK, fair point.  ;-)

							Thanx, Paul