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



On 08/25/2012 06:24 AM, Mathieu Desnoyers wrote:
> * Tejun Heo (tj kernel org) wrote:
>> Hello,
>>
>> On Sat, Aug 25, 2012 at 12:59:25AM +0200, Sasha Levin wrote:
>>> Thats the thing, the amount of things of things you can do with a given bucket
>>> is very limited. You can't add entries to any point besides the head (without
>>> walking the entire list).
>>
>> Kinda my point.  We already have all the hlist*() interface to deal
>> with such cases.  Having something which is evidently the trivial
>> hlist hashtable and advertises as such in the interface can be
>> helpful.  I think we need that more than we need anything fancy.
>>
>> Heh, this is a debate about which one is less insignificant.  I can
>> see your point.  I'd really like to hear what others think on this.
>>
>> Guys, do we want something which is evidently trivial hlist hashtable
>> which can use hlist_*() API directly or do we want something better
>> encapsulated?
> 
> My 2 cents, FWIW: I think this specific effort should target a trivially
> understandable API and implementation, for use-cases where one would be
> tempted to reimplement his own trivial hash table anyway. So here
> exposing hlist internals, with which kernel developers are already
> familiar, seems like a good approach in my opinion, because hiding stuff
> behind new abstraction might make the target users go away.
> 
> Then, as we see the need, we can eventually merge a more elaborate hash
> table with poneys and whatnot, but I would expect that the trivial hash
> table implementation would still be useful. There are of course very
> compelling reasons to use a more featureful hash table: automatic
> resize, RT-aware updates, scalable updates, etc... but I see a purpose
> for a trivial implementation. Its primary strong points being:
> 
> - it's trivially understandable, so anyone how want to be really sure
>   they won't end up debugging the hash table instead of their
>   work-in-progress code can have a full understanding of it,
> - it has few dependencies, which makes it easier to understand and
>   easier to use in some contexts (e.g. early boot).
> 
> So I'm in favor of not overdoing the abstraction for this trivial hash
> table, and honestly I would rather prefer that this trivial hash table
> stays trivial. A more elaborate hash table should probably come as a
> separate API.
> 
> Thanks,
> 
> Mathieu
> 

Alright, let's keep it simple then.

I do want to keep the hash_for_each[rcu,safe] family though.


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