On Wed, Mar 06, 2013 at 03:21:50PM -0800, Michel Lespinasse wrote: > When the first queued waiter is a reader, wake all readers instead of > just those that are at the front of the queue. There are really two > motivations for this change:
Isn't this a significant change of semantics for the rwsem? i.e. that read lock requests that come after a write lock request now jump ahead of the write lock request? i.e.the write lock request is no longer a barrier in the queue? XFS has long assumed that a rwsem write lock is a barrier that stops new read locks from being taken, and this change will break that assumption. Given that this barrier assumption is used as the basis for serialisation of operations like IO vs truncate, there's a bit more at stake than just improving parallelism here. i.e. IO issued after truncate/preallocate/hole punch could now be issued ahead of the pending metadata operation, whereas currently the IO issued after the pending metadata operation is waiting for the write lock will be only be processed -after- the metadata modification operation completes... That is a recipe for weird data corruption problems because applications are likely to have implicit dependencies on the barrier effect of metadata operations on data IO... Cheers, Dave. -- Dave Chinner da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/