From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940728AbdAFWni (ORCPT ); Fri, 6 Jan 2017 17:43:38 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:60944 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S939589AbdAFWn0 (ORCPT ); Fri, 6 Jan 2017 17:43:26 -0500 Date: Fri, 6 Jan 2017 14:43:48 -0800 From: Andrew Morton To: Paul Burton Cc: , James Hartley , Subject: Re: [PATCH] mm: page_alloc: Skip over regions of invalid pfns where possible Message-Id: <20170106144348.f7d207baa7b3190a95aaeb2e@linux-foundation.org> In-Reply-To: <20161125185518.29885-1-paul.burton@imgtec.com> References: <20161125185518.29885-1-paul.burton@imgtec.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 25 Nov 2016 18:55:18 +0000 Paul Burton wrote: > When using a sparse memory model memmap_init_zone() when invoked with > the MEMMAP_EARLY context will skip over pages which aren't valid - ie. > which aren't in a populated region of the sparse memory map. However if > the memory map is extremely sparse then it can spend a long time > linearly checking each PFN in a large non-populated region of the memory > map & skipping it in turn. > > When CONFIG_HAVE_MEMBLOCK_NODE_MAP is enabled, we have sufficient > information to quickly discover the next valid PFN given an invalid one > by searching through the list of memory regions & skipping forwards to > the first PFN covered by the memory region to the right of the > non-populated region. Implement this in order to speed up > memmap_init_zone() for systems with extremely sparse memory maps. Could we have a changelog which includes some timing measurements? That permits others to understand the value of this patch.