On Mon 11-02-13 03:03:30, Michel Lespinasse wrote: > On Mon, Feb 11, 2013 at 2:27 AM, Jan Kara <jack@xxxxxxx> wrote: > > On Sun 10-02-13 21:42:32, Michel Lespinasse wrote: > >> On Thu, Jan 31, 2013 at 1:49 PM, Jan Kara <jack@xxxxxxx> wrote: > >> > +void range_lock_init(struct range_lock *lock, unsigned long start, > >> > + unsigned long end); > >> > +void range_lock(struct range_lock_tree *tree, struct range_lock *lock); > >> > +void range_unlock(struct range_lock_tree *tree, struct range_lock *lock); > >> > >> Is there a point to separating the init and lock stages ? maybe the API could be > >> void range_lock(struct range_lock_tree *tree, struct range_lock *lock, > >> unsigned long start, unsigned long last); > >> void range_unlock(struct range_lock_tree *tree, struct range_lock *lock); > > I was thinking about this as well. Currently I don't have a place which > > would make it beneficial to separate _init and _lock but I can imagine such > > uses (where you don't want to pass the interval information down the stack > > and it's easier to pass the whole lock structure). Also it looks a bit > > confusing to pass (tree, lock, start, last) to the locking functon. So I > > left it there. > > > > OTOH I had to somewhat change the API so that the locking phase is now > > separated in "lock_prep" phase which inserts the node into the tree and > > counts blocking ranges and "wait" phase which waits for the blocking ranges > > to unlock. The reason for this split is that while "lock_prep" needs to > > happen under some lock synchronizing operations on the tree, "wait" phase > > can be easily lockless. So this allows me to remove the knowledge of how > > operations on the tree are synchronized from range locking code itself. > > That further allowed me to use mapping->tree_lock for synchronization and > > basically reduce the cost of mapping range locking close to 0 for buffered > > IO (just a single tree lookup in the tree in the fast path). > > Ah yes, being able to externalize the lock is good. > > I think in this case, it makes the most sense for lock_prep phase to > also initialize the lock node, though. I guess so. > >> Reviewed-by: Michel Lespinasse <walken@xxxxxxxxxx> > > I actually didn't add this because there are some differences in the > > current version... > > Did I miss another posting of yours, or is that coming up ? That will come. But as Dave Chinner pointed out for buffered writes we should rather lock the whole range specified in the syscall (to avoid strange results of racing truncate / write when i_mutex isn't used) and that requires us to put the range lock above mmap_sem which isn't currently easily possible due to page fault handling... So if the whole patch set should go anywhere I need to solve that somehow. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
