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Date: Sat, 16 Oct 2010 18:57:03 +1100
From: Nick Piggin <npiggin@kernel.dk>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 11/18] fs: Introduce per-bucket inode hash locks
Message-ID: <20101016075703.GO19147@amd>
References: <1286515292-15882-1-git-send-email-david@fromorbit.com>
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 <20101008185409.GA29251@infradead.org>
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On Fri, Oct 08, 2010 at 02:54:09PM -0400, Christoph Hellwig wrote:
> > +struct inode_hash_bucket {
> > +	struct hlist_bl_head head;
> > +};
> > +
> > +static inline void spin_lock_bucket(struct inode_hash_bucket *b)
> > +{
> > +	bit_spin_lock(0, (unsigned long *)b);
> > +}
> > +
> > +static inline void spin_unlock_bucket(struct inode_hash_bucket *b)
> > +{
> > +	__bit_spin_unlock(0, (unsigned long *)b);
> > +}
> 
> I've looked at the dcache version of this again, and I really hate
> 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.