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

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Date:	Sun, 17 Oct 2010 04:12:13 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/18] fs: Introduce per-bucket inode hash locks

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.

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