Re: [PATCH 11/18] fs: Introduce per-bucket inode hash locks

Nick Piggin
2010-10-16T17:12:16Z

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.

> So if e.g. the -rt folks need
> real locks in there there is one single place they need to touch
> instead of every user. Similarly if we want to add lockdep support
> there is just one place to touch.

It's unnecessary.