From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753657Ab2HCVgY (ORCPT ); Fri, 3 Aug 2012 17:36:24 -0400 Received: from mail-wi0-f178.google.com ([209.85.212.178]:50126 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753110Ab2HCVgW (ORCPT ); Fri, 3 Aug 2012 17:36:22 -0400 Message-ID: <501C4471.4090706@gmail.com> Date: Fri, 03 Aug 2012 23:36:49 +0200 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120730 Thunderbird/14.0 MIME-Version: 1.0 To: Tejun Heo 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 Subject: Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable References: <1344003788-1417-1-git-send-email-levinsasha928@gmail.com> <1344003788-1417-2-git-send-email-levinsasha928@gmail.com> <20120803171515.GH15477@google.com> <501C407D.9080900@gmail.com> <20120803213017.GK15477@google.com> In-Reply-To: <20120803213017.GK15477@google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/03/2012 11:30 PM, Tejun Heo wrote: >> 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. The function definition itself is just a macro, for example: #define MM_SLOTS_HASH_CMP(mm_slot, obj) ((mm_slot)->mm == (obj)) As an alternative, what do you think about simplifying that to be just a 'cond' instead of a function? Something like: hash_get(&mm_slots_hash, mm, struct mm_slot, hash, mm); In that case, the last param ("mm") will get unrolled to a condition like this: if ((obj)->mm == key) Which will be simple and easy for the user. The only reason I want to keep this interface is that most cases I've stumbled so far were easy short comparisons of a struct member with the key, and I don't want to make them more complex than they need to be. I probably will switch hash_get() to use hash_for_each_possible() as well, which will cut down on how hash_get() is a separate case.