From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx201.postini.com [74.125.245.201]) by kanga.kvack.org (Postfix) with SMTP id 4E0BF6B005A for ; Mon, 29 Oct 2012 11:13:45 -0400 (EDT) Date: Mon, 29 Oct 2012 11:13:43 -0400 From: Mathieu Desnoyers Subject: Re: [PATCH v7 09/16] SUNRPC/cache: use new hashtable implementation Message-ID: <20121029151343.GA17722@Krystal> References: <1351450948-15618-1-git-send-email-levinsasha928@gmail.com> <1351450948-15618-9-git-send-email-levinsasha928@gmail.com> <20121029124229.GC11733@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Sasha Levin , tj@kernel.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, 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 * Linus Torvalds (torvalds@linux-foundation.org) wrote: > On Mon, Oct 29, 2012 at 5:42 AM, Mathieu Desnoyers > wrote: > > > > So defining e.g.: > > > > #include > > > > #define DFR_HASH_BITS (PAGE_SHIFT - ilog2(BITS_PER_LONG)) > > > > would keep the intended behavior in all cases: use one page for the hash > > array. > > Well, since that wasn't true before either because of the long-time > bug you point out, clearly the page size isn't all that important. I > think it's more important to have small and simple code, and "9" is > certainly that, compared to playing ilog2 games with not-so-obvious > things. > > Because there's no reason to believe that '9' is in any way a worse > random number than something page-shift-related, is there? And getting > away from *previous* overly-complicated size calculations that had > been broken because they were too complicated and random, sounds like > a good idea. Good point. I agree that unless we really care about the precise number of TLB entries and cache lines used by this hash table, we might want to stay away from page-size and pointer-size based calculation. It might not hurt to explain this in the patch changelog though. Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- 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