From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx168.postini.com [74.125.245.168]) by kanga.kvack.org (Postfix) with SMTP id 30BE96B004D for ; Thu, 2 Aug 2012 12:47:41 -0400 (EDT) Received: by bkcjc3 with SMTP id jc3so5283654bkc.14 for ; Thu, 02 Aug 2012 09:47:39 -0700 (PDT) Message-ID: <501AAF47.3090708@gmail.com> Date: Thu, 02 Aug 2012 18:48:07 +0200 From: Sasha Levin MIME-Version: 1.0 Subject: Re: [RFC 1/4] hashtable: introduce a small and naive hashtable References: <50197460.8010906@gmail.com> <20120801182749.GD15477@google.com> <50197E4A.7020408@gmail.com> <20120801202432.GE15477@google.com> <5019B0B4.1090102@gmail.com> <20120801224556.GF15477@google.com> <501A4FC1.8040907@gmail.com> <20120802103244.GA23318@leaf> <501A633B.3010509@gmail.com> <501A7AD3.7000008@gmail.com> <20120802161556.GA25572@leaf> In-Reply-To: <20120802161556.GA25572@leaf> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Josh Triplett Cc: Tejun Heo , torvalds@linux-foundation.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, paul.gortmaker@windriver.com On 08/02/2012 06:15 PM, Josh Triplett wrote: > On Thu, Aug 02, 2012 at 03:04:19PM +0200, Sasha Levin wrote: >> On 08/02/2012 01:23 PM, Sasha Levin wrote: >>>> #define DEFINE_HASH_TABLE(name, length) struct hash_table name = { .count = length, .buckets = { [0 ... (length - 1)] = HLIST_HEAD_INIT } } >>> The limitation of this approach is that the struct hash_table variable must be 'static', which is a bit limiting - see for example the use of hashtable in 'struct user_namespace'. >>> >> >> What if we just use two possible decelerations? One of static structs and one for regular ones. >> >> struct hash_table { >> size_t bits; >> struct hlist_head buckets[]; >> }; >> >> #define DEFINE_HASHTABLE(name, bits) \ >> union { \ >> struct hash_table name; \ >> struct { \ >> size_t bits; \ > > This shouldn't use "bits", since it'll get expanded to the macro > argument. > >> struct hlist_head buckets[1 << bits]; \ >> } __name; \ > > __##name > >> } >> >> #define DEFINE_STATIC_HASHTABLE(name, bit) \ >> static struct hash_table name = { .bits = bit, \ >> .buckets = { [0 ... (bit - 1)] = HLIST_HEAD_INIT } } > > You probably wanted to change that to [0 ... ((1 << bit) - 1)] , to > match DEFINE_HASHTABLE. I wrote it by hand and didn't compile test, will fix all of those. > Since your definition of DEFINE_HASHTABLE would also work fine when used > statically, why not just always use that? > > #define DEFINE_STATIC_HASHTABLE(name, bits) static DEFINE_HASHTABLE(name, bits) = { .name.bits = bits } It will get defined fine, but it will be awkward to use. We'd need to pass anonymous union to all the functions that handle this hashtable, which isn't pretty. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org