From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx152.postini.com [74.125.245.152]) by kanga.kvack.org (Postfix) with SMTP id 1CBCF6B0044 for ; Fri, 3 Aug 2012 18:19:37 -0400 (EDT) Received: by bkcjc3 with SMTP id jc3so585489bkc.14 for ; Fri, 03 Aug 2012 15:19:35 -0700 (PDT) Message-ID: <501C4E92.1070801@gmail.com> Date: Sat, 04 Aug 2012 00:20:02 +0200 From: Sasha Levin MIME-Version: 1.0 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> <501C458E.7050000@gmail.com> <20120803214806.GM15477@google.com> In-Reply-To: <20120803214806.GM15477@google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 On 08/03/2012 11:48 PM, Tejun Heo wrote: > Hello, > > On Fri, Aug 03, 2012 at 11:41:34PM +0200, Sasha Levin wrote: >> I forgot to comment on that one, sorry. >> >> If we put hash entries after struct hash_table we don't take the >> bits field size into account, or did I miss something? > > So, if you do the following, > > struct { > struct { > int i; > long ar[]; > } B; > long __ar_storage[32]; > } A; struct A should have been an union, right? > It should always be safe to dereference A.B.ar[31]. I'm not sure > whether this is something guaranteed by C tho. Maybe compilers are > allowed to put members in reverse order but I think we already depend > on the above. why is accessing A.B.ar[31] safe? __ar_storage is only 32*sizeof(long) bytes long, while struct B would need to be 32*sizeof(long) + sizeof(int) bytes long so that A.B.ar[31] access would be safe. > Thanks. > -- 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