From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753491Ab2HWUFF (ORCPT ); Thu, 23 Aug 2012 16:05:05 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:39908 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752667Ab2HWUFB (ORCPT ); Thu, 23 Aug 2012 16:05:01 -0400 Date: Thu, 23 Aug 2012 13:04:56 -0700 From: Tejun Heo To: Sasha Levin Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, paul.gortmaker@windriver.com, davem@davemloft.net, rostedt@goodmis.org, mingo@elte.hu, ebiederm@xmission.com, aarcange@redhat.com, ericvh@gmail.com, netdev@vger.kernel.org, josh@joshtriplett.org, eric.dumazet@gmail.com, mathieu.desnoyers@efficios.com, axboe@kernel.dk, agk@redhat.com, dm-devel@redhat.com, neilb@suse.de, ccaulfie@redhat.com, teigland@redhat.com, Trond.Myklebust@netapp.com, bfields@fieldses.org, fweisbec@gmail.com, jesse@nicira.com, venkat.x.venkatsubra@oracle.com, ejt@redhat.com, snitzer@redhat.com, edumazet@google.com, linux-nfs@vger.kernel.org, dev@openvswitch.org, rds-devel@oss.oracle.com, lw@cn.fujitsu.com Subject: Re: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable Message-ID: <20120823200456.GD14962@google.com> References: <1345602432-27673-1-git-send-email-levinsasha928@gmail.com> <1345602432-27673-2-git-send-email-levinsasha928@gmail.com> <20120822180138.GA19212@google.com> <50357840.5020201@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50357840.5020201@gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Sasha. On Thu, Aug 23, 2012 at 02:24:32AM +0200, Sasha Levin wrote: > > I think the almost trivial nature of hlist hashtables makes this a bit > > tricky and I'm not very sure but having this combinatory explosion is > > a bit dazzling when the same functionality can be achieved by simply > > combining operations which are already defined and named considering > > hashtable. I'm not feeling too strong about this tho. What do others > > think? > > I'm thinking that this hashtable API will have 2 purposes: First, it would > prevent the excessive duplication of hashtable implementations all around the code. > > Second, it will allow more easily interchangeable hashtable implementations to > find their way into the kernel. There are several maintainers who would be happy > to see dynamically sized RCU hashtable, and I'm guessing that several more > variants could be added based on needs in specific modules. > > The second reason is why several things you've mentioned look the way they are: > > - No DEFINE_HASHTABLE(): I wanted to force the use of hash_init() since > initialization for other hashtables may be more complicated than the static > initialization for this implementation, which means that any place that used > DEFINE_HASHTABLE() and didn't do hash_init() will be buggy. 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'm actually tempted in hiding hlist completely from hashtable users, probably > by simply defining a hash_head/hash_node on top of the hlist_ counterparts. I think that it would be best to keep this one simple & obvious, which already has enough in-kernel users to justify its existence. There are significant benefits in being trivially understandable and expectable. If we want more advanced ones - say resizing, hybrid or what not, let's make that a separate one. No need to complicate the common straight-forward case for that. 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. Thanks. -- tejun