linux-kernel - Re: [PATCH v2 01/16] hashtable: introduce a small and naive hashtable

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Message-ID: <20120819141641.GA9082@Krystal>
Date:	Sun, 19 Aug 2012 10:16:41 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, tj@...nel.org,
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Subject: Re: [PATCH v2 01/16] hashtable: introduce a small and naive
	hashtable

* Mathieu Desnoyers (mathieu.desnoyers@...icios.com) wrote:
> * Sasha Levin (levinsasha928@...il.com) wrote:
[...]
> > +/**
> > + * hash_for_each_possible - iterate over all possible objects for a given key
> > + * @name: hashtable to iterate
> > + * @obj: the type * to use as a loop cursor for each bucket
> > + * @bits: bit count of hashing function of the hashtable
> > + * @node: the &struct list_head to use as a loop cursor for each bucket
> > + * @member: the name of the hlist_node within the struct
> > + * @key: the key of the objects to iterate over
> > + */
> > +#define hash_for_each_possible_size(name, obj, bits, node, member, key)		\
> > +	hlist_for_each_entry(obj, node,	&name[hash_min(key, bits)], member)
> 
> Second point: "for_each_possible" does not express the iteration scope.
> Citing WordNet: "possible adj 1: capable of happening or existing;" --
> which has nothing to do with iteration on duplicate keys within a hash
> table.
> 
> I would recommend to rename "possible" to "duplicate", e.g.:
> 
>   hash_for_each_duplicate()
> 
> which clearly says what is the scope of this iteration: duplicate keys.

OK, about this part: I now see that you iterate over all objects within
the same hash chain. I guess the description "iterate over all possible
objects for a given key" is misleading: it's not all objects with a
given key, but rather all objects hashing to the same bucket.

I understand that you don't want to build knowledge of the key
comparison function in the iterator (which makes sense for a simple hash
table).

By the way, the comment "@obj: the type * to use as a loop cursor for
each bucket" is also misleading: it's a loop cursor for each entry,
since you iterate on all nodes within single bucket. Same for "@node:
the &struct list_head to use as a loop cursor for each bucket".

So with these documentation changes applied, hash_for_each_possible
starts to make more sense, because it refers to entries that can
_possibly_ be a match (or not). Other options would be
hash_chain_for_each() or hash_bucket_for_each().

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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