From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S970676AbdAEMI4 (ORCPT ); Thu, 5 Jan 2017 07:08:56 -0500 Received: from foss.arm.com ([217.140.101.70]:49464 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757098AbdAEMIq (ORCPT ); Thu, 5 Jan 2017 07:08:46 -0500 Date: Thu, 5 Jan 2017 12:08:20 +0000 From: Will Deacon To: Robert Richter Cc: Ard Biesheuvel , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Catalin Marinas , Andrew Morton , Hanjun Guo , Yisheng Xie , James Morse Subject: Re: [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA Message-ID: <20170105120819.GH679@arm.com> References: <1481706707-6211-1-git-send-email-ard.biesheuvel@linaro.org> <1481706707-6211-3-git-send-email-ard.biesheuvel@linaro.org> <20170104132831.GD18193@arm.com> <20170104140223.GF18193@arm.com> <20170105112407.GU4930@rric.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170105112407.GU4930@rric.localdomain> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 05, 2017 at 12:24:07PM +0100, Robert Richter wrote: > On 04.01.17 14:02:23, Will Deacon wrote: > > Using early_pfn_valid feels like a bodge to me, since having pfn_valid > > return false for something that early_pfn_valid says is valid (and is > > therefore initialised in the memmap) makes the NOMAP semantics even more > > confusing. > > The concern I have had with HOLES_IN_ZONE is that it enables > pfn_valid_within() for arm64. This means that each pfn of a section is > checked which is done only once for the section otherwise. With up to > 2^18 pages per section we traverse the memblock list by that factor > more often. There could be a performance regression. There could be, but we're trying to fix a bug here. I wouldn't have thought that walking over pfns like that is done very often. > I haven't numbers yet, since the fix causes another kernel crash. And, > this is the next problem I have. The crash doesn't happen otherwise. So, > either it uncovers another bug or the fix is incomplete. Though the > changes look like it should work. This needs more investigation. I really can't see how the fix causes a crash, and I couldn't reproduce it on any of my boards, nor could any of the Linaro folk afaik. Are you definitely running mainline with just these two patches from Ard? Will