linux-kernel - Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

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Message-ID: <20120803213017.GK15477@google.com>
Date:	Fri, 3 Aug 2012 14:30:17 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paul.gortmaker@...driver.com, davem@...emloft.net,
	rostedt@...dmis.org, mingo@...e.hu, ebiederm@...ssion.com,
	aarcange@...hat.com, ericvh@...il.com, netdev@...r.kernel.org
Subject: Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

Hello,

On Fri, Aug 03, 2012 at 11:19:57PM +0200, Sasha Levin wrote:
> > Is this supposed to be embedded in struct definition?  If so, the name
> > is rather misleading as DEFINE_* is supposed to define and initialize
> > stand-alone constructs.  Also, for struct members, simply putting hash
> > entries after struct hash_table should work.
> 
> It would work, but I didn't want to just put them in the union since
> I feel it's safer to keep them in a separate struct so they won't be
> used by mistake,

Just use ugly enough pre/postfixes.  If the user still accesses that,
it's the user's fault.

> >> +static void hash_init(struct hash_table *ht, size_t bits)
> >> +{
> >> +	size_t i;
> > 
> > I would prefer int here but no biggie.
> 
> Just wondering, is there a particular reason behind it?

It isn't a size and using unsigned when signed suffices seems to cause
more headache than helps anything usually due to lack of values to use
for exceptional conditions (usually -errno or -1).

> > As opposed to using hash_for_each_possible(), how much difference does
> > this make?  Is it really worthwhile?
> 
> Most of the places I've switched to using this hashtable so far (4
> out of 6) are using hash_get(). I think that the code looks cleaner
> when you an just provide a comparison function instead of
> implementing the iteration itself.
>
> I think hash_for_for_each_possible() is useful if the comparison
> condition is more complex than a simple comparison of one of the
> object members with the key - there's no need to force it on all the
> users.

I don't know.  What's the difference?  In terms of LOC, it might even
not save any thanks to the extra function definition, right?  I don't
think it's saving enough complexity to justify a separate rather
unusual interface.

Thanks.

-- 
tejun
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