On Fri, Dec 07, 2012 at 10:18:00AM -0800, Linus Torvalds wrote: > > And that's _fine_. Once you have actual technical arguments ("I'd like to > re-appropriate that bit, because xyzzy") you have real and valid > arguments, and it would be easy to then do the sane "let's just use the > bit for something more worthy" thing. But even then it's nice to have the > knowledge about what the implications of such use would be, for chrissake! First I want to say that I don't really give a crap about this bit, and whether or not it's been merged or not. But I think Ric did have one valid point: >> I would prefer to fix the performance issue in ext4 rather than add an >> interface that has no actual users of the actual feature - it exists >> for applications that want to avoid an unfortunate performance hit >> from something that we could work around. This is similar to the preemptible big kernel lock. The BKL has been an issue for almost everyone, and a really big one for the real-time folks. But because it was converted into a preemtible lock, it was dropped low on the priority list of things to get fixed. But it wasn't until you reverted this code to kick our ass into gear to go about and fix the issue. How is this similar? By adding this bit, we removed incentive from a group of developers that have the means to fix the real issue at hand (the performance problem with ext4). Thus, it means that they have a work around that's good enough for them, but the rest of us suffer. Sure, they could just modify their kernel to keep this bit, but as it wouldn't be reserved, they would have to worry about colisions in the future. Thus the incentive to fix the problem at hand. Just like we had the preempt BKL in the real-time patch, but it was just better to get it fixed in mainline. Thanks to Frederic that started the work, and then Arnd that finished it, we no longer have that nasty lock around to deal with. You were very wise to revert the preemptible BKL, as I believe we probably would still have BKL in the kernel if you didn't do that. Maybe reverting this bit might do the same thing? Maybe not. It's your call. -- Steve -- 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