On Sat, 2015-04-18 at 00:02 +0100, Al Viro wrote: > On Sat, Apr 18, 2015 at 12:16:48AM +0200, Mateusz Guzik wrote: > > > I would say this makes the use of seq counter impossible. Even if we > > decided to fall back to a lock on retry, we cannot know what to do if > > the slot is reserved - it very well could be that something called > > close, and something else reserved the slot, so putting the file inside > > could be really bad. In fact we would be putting a file for which we > > don't have a reference anymore. > > > > However, not all hope is lost and I still think we can speed things up. > > > > A locking primitive which only locks stuff for current cpu and has > > another mode where it locks stuff for all cpus would do the trick just > > fine. I'm not a linux guy, quick search suggests 'lglock' would do what > > I want. > > > > table reallocation is an extremely rare operation, so this should be > > fine. It would take the lock 'globally' for given table. > > It would also mean percpu_alloc() for each descriptor table... I would rather use an xchg() instead of rcu_assign_ponter() old = xchg(&fdt->fd[fd], file); if (unlikely(old)) filp_close(old, files); If threads are using close() on random fds, final result is not guaranteed anyway. -- 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
