On Fri, Aug 31, 2007 at 05:09:21PM +0200, Peter Zijlstra wrote: > On Sat, 2007-09-01 at 01:05 +1000, David Chinner wrote: > > > > Trouble is, we'd like to have a sane upper bound on the amount of held > > > locks at any one time, obviously this is just wanting, because a lot of > > > lock chains also depend on the number of online cpus... > > > > Sure - this is an obvious case where it is valid to take >30 locks at > > once in a single thread. In fact, worst case here we are taking twice this > > number of locks - we actually take 2 per inode (ilock and flock) so a > > full 32 inode cluster free would take >60 locks in the middle of this > > function and we should be busting this depth couter limit all the > > time. > > I think this started because jeffpc couldn't boot without XFS busting > lockdep :-)
Ok.... > > Do semaphores (the flush locks) contribute to the lock depth > > counters? > > No, alas, we cannot handle semaphores in lockdep. Semaphores don't have > a strict owner, hence we cannot track them. This is one of the reasons > to rid ourselves of semaphores - that and there are very few cases where > the actual semantics of semaphores are needed. Most of the times code > using semaphores can be expressed with either a mutex or a completion. Yeah, and the flush lock is something we can't really use either of those for as we require both the multi-process lock/unlock behaviour and the mutual exclusion that a semaphore provides. So I guess that means it's only the ilock nesting that is of issue here, so that means right now a max lock depth of 40 would probably be ok.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
