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Re: [dm-devel] [PATCH v3 01/17] hashtable: introduce a small and naive hashtable



On 08/24/2012 09:59 PM, Tejun Heo wrote:
> Hello, Sasha.
> 
> On Fri, Aug 24, 2012 at 09:47:19PM +0200, Sasha Levin wrote:
>>> I think this is problematic.  It looks exactly like other existing
>>> DEFINE macros yet what its semantics is different.  I don't think
>>> that's a good idea.
>>
>> I can switch that to be DECLARE_HASHTABLE() if the issue is semantics.
> 
> If this implementation is about the common trivial case, why not just
> have the usual DECLARE/DEFINE_HASHTABLE() combination?

When we add the dynamic non-resizable support, how would DEFINE_HASHTABLE() look?

>>> So, I think it would be best to keep this one as straight-forward and
>>> trivial as possible.  Helper macros to help its users are fine but
>>> let's please not go for full encapsulation.
>>
>> What if we cut off the dynamic allocated (but not resizable) hashtable out for
>> the moment, and focus on the most common statically allocated hashtable case?
>>
>> The benefits would be:
>>
>>  - Getting rid of all the _size() macros, which will make the amount of helpers
>> here reasonable.
>>  - Dynamically allocated hashtable can be easily added as a separate
>> implementation using the same API. We already have some of those in the kernel...
> 
> It seems we have enough of this static usage and solving the static
> case first shouldn't hinder the dynamic (!resize) case later, so,
> yeah, sounds good to me.
> 
>>  - When that's ready, I feel it's a shame to lose full encapsulation just due to
>> hash_hashed().
> 
> I don't know.  If we stick to the static (or even !resize dymaic)
> straight-forward hash - and we need something like that - I don't see
> what the full encapsulation buys us other than a lot of trivial
> wrappers.

Which macros do you consider as trivial within the current API?

Basically this entire thing could be reduced to DEFINE/DECLARE_HASHTABLE and
get_bucket(), but it would make the life of anyone who wants a slightly
different hashtable a hell.

I think that right now the only real trivial wrapper is hash_hashed(), and I
think it's a price worth paying to have a single hashtable API instead of
fragmenting it when more implementations come along.

Thanks,
Sasha

> 
> Thanks.
> 


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