On Sun, Oct 17, 2010 at 11:46:10AM +1100, Dave Chinner wrote: > On Sun, Oct 17, 2010 at 04:12:13AM +1100, Nick Piggin wrote: > > On Sat, Oct 16, 2010 at 12:16:42PM -0400, Christoph Hellwig wrote: > > > On Sat, Oct 16, 2010 at 06:57:03PM +1100, Nick Piggin wrote: > > > > > duplicating these helpers in the dcache code aswell. IMHO they > > > > > should simple operate directly on the hlist_bl_head, as that's > > > > > what it was designed for. I also don't really see any point in > > > > > wrapping the hlist_bl_head as inode_hash_bucket. If the bucket naming > > > > > is important we could rename the hlist_bl stuff to bl_hash, and the > > > > > hlist_bl_head could become bl_hash_bucket. > > > > > > > > It was done because someone, like -rt, might want more than one bit of > > > > memory to implement a lock. They would have to make a few other > > > > changes, granted, but this helps reduce a lot of churn. > > > > > > > > I didn't see the point of a layer of dumb wrappers for hlist_bl_head > > > > locking. Just reproducing bit spin and wait locks in wrappers when we > > > > already have good functions for them. > > > > > > With the changes Dave implemented based on my suggestions we now have > > > an abstract locked hash list data type. It has the normal hash list > > > operations plus lock/unlock operations. > > > > That's ugly. It just hides the locking. If a bit of casting bothers > > you then put it in a function where it is used like I did. > > I much prefer the abstraction from an end-user point of view. Asking > every developer to understand the intricacies of locking the > hlist_bl structures is asking them to get it wrong. Asking them to understand that 0 bit is to be used for locking? If they don't understand that they shouldn't be doing kernel programming, let alone trying to implement advanced scalability with bl lists. Really. > Providing > locking wrappers that are exactly what users need so they don't have > to care about it is, IMO, the right thing to do. Hiding the type of lock, and hiding the fact that it sets the low bit? I don't agree. We don't have synchronization in our data structures, where possible, because it is just restrictive or goes wrong when people don't think enough about the locking. -- 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
