From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763045AbdDSMhs (ORCPT ); Wed, 19 Apr 2017 08:37:48 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:42845 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762733AbdDSMhq (ORCPT ); Wed, 19 Apr 2017 08:37:46 -0400 Date: Wed, 19 Apr 2017 14:37:35 +0200 From: Peter Zijlstra To: Davidlohr Bueso Cc: mingo@kernel.org, akpm@linux-foundation.org, jack@suse.cz, kirill.shutemov@linux.intel.com, ldufour@linux.vnet.ibm.com, mhocko@suse.com, mgorman@techsingularity.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 -tip 0/6] locking: Introduce range reader/writer lock Message-ID: <20170419123735.GB5730@worktop> References: <20170406084620.22700-1-dave@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170406084620.22700-1-dave@stgolabs.net> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 06, 2017 at 01:46:14AM -0700, Davidlohr Bueso wrote: > ** What's still pending: > - Debug support (it's been a pain to use lockdep with range locking). How so? Just assume that every range is the full range. Which isn't such a weird assumption as it would seem. After all, you cannot assume anything much about the ranges to begin with. So therefore you cannot assume the ranges don't all overlap either. At which point you're back to the regular r/w semantics for deadlocks. Also: - explain interval order and what that means for forward progress guarantees. This is currently still unparsable. - explain why the loss of lock stealing makes sense. IIRC walken added that specifically to address mmap_sem performance issues.