From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752158AbdBKCZT (ORCPT ); Fri, 10 Feb 2017 21:25:19 -0500 Received: from mail-qk0-f193.google.com ([209.85.220.193]:33517 "EHLO mail-qk0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751503AbdBKCZS (ORCPT ); Fri, 10 Feb 2017 21:25:18 -0500 Date: Sat, 11 Feb 2017 11:24:00 +0900 From: Tejun Heo To: Wei Yang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 2/2] mm/sparse: add last_section_nr in sparse_init() to reduce some iteration cycle Message-ID: <20170211022400.GA19050@mtj.duckdns.org> References: <20170211021829.9646-1-richard.weiyang@gmail.com> <20170211021829.9646-2-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170211021829.9646-2-richard.weiyang@gmail.com> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Sat, Feb 11, 2017 at 10:18:29AM +0800, Wei Yang wrote: > During the sparse_init(), it iterate on each possible section. On x86_64, > it would always be (2^19) even there is not much memory. For example, on a > typical 4G machine, it has only (2^5) to (2^6) present sections. This > benefits more on a system with smaller memory. > > This patch calculates the last section number from the highest pfn and use > this as the boundary of iteration. * How much does this actually matter? Can you measure the impact? * Do we really need to add full reverse iterator to just get the highest section number? Thanks. -- tejun