Le mardi 09 novembre 2010 Ã 08:02 -0800, Linus Torvalds a Ãcrit : > On Tue, Nov 9, 2010 at 4:46 AM, Nick Piggin <npiggin@xxxxxxxxx> wrote: > > So here is the inode RCU code. It's obviously not worth doing until the > > actual rcu-walk path walking is in, but I'd like to get opinions on it. > > It would be nice to merge it in Al's tree at some point, though. > > Remind me why it wasn't sufficient to just use SLAB_DESTROY_BY_RCU? > > Especially if we still lock things for the actual (few) inode list > operations, the added complexity of actually freeing _individual_ > inodes by RCU seems to be a bad thing. > > The only thing we care about is the pathname walk - there are no other > inode operations that are common enough to worry about. And the only > thing _that_ needs is the ability to look at the inode under RCU, and > SLAB_DESTROY_BY_RCU should be entirely sufficient for that. > > But we had some discussion about this long ago, and I may have > forgotten some of the context. > David Chinner sent a patch using SLAB_DESTROY_BY_RCU You can see problems using this fancy thing : - Need to use slab ctor() to not overwrite some sensitive fields of reused inodes. (spinlock, next pointer) - Fancy algo to detect an inode moved from one chain to another. Lookups should be able to detect and restart their loop. - After a match, need to get a stable reference on inode (lock), then recheck the keys to make sure the target inode is the right one. http://www.gossamer-threads.com/lists/linux/kernel/1298710 A bit tricky, but doable IMHO, especially if covering only the main lookup. The seldom used can still get a (spin)lock. -- 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
