From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751458Ab3IJKei (ORCPT ); Tue, 10 Sep 2013 06:34:38 -0400 Received: from terminus.zytor.com ([198.137.202.10]:39069 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751011Ab3IJKeg (ORCPT ); Tue, 10 Sep 2013 06:34:36 -0400 Date: Tue, 10 Sep 2013 03:34:15 -0700 From: tip-bot for Yinghai Lu Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, yinghai@kernel.org, penberg@kernel.org, jacob.shin@amd.com, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, yinghai@kernel.org, penberg@kernel.org, jacob.shin@amd.com, tglx@linutronix.de In-Reply-To: <1378519629-10433-1-git-send-email-yinghai@kernel.org> References: <1378519629-10433-1-git-send-email-yinghai@kernel.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/mm] x86/mm: Add 'step_size' comments to init_mem_mapping () Git-Commit-ID: 6979287a7df66a92d6f308338e972a406f9ef842 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (terminus.zytor.com [127.0.0.1]); Tue, 10 Sep 2013 03:34:25 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 6979287a7df66a92d6f308338e972a406f9ef842 Gitweb: http://git.kernel.org/tip/6979287a7df66a92d6f308338e972a406f9ef842 Author: Yinghai Lu AuthorDate: Fri, 6 Sep 2013 19:07:09 -0700 Committer: Ingo Molnar CommitDate: Tue, 10 Sep 2013 09:51:34 +0200 x86/mm: Add 'step_size' comments to init_mem_mapping() Current code uses macro to shift by 5, but there is no explanation why there's no worry about an overflow there. Signed-off-by: Yinghai Lu Cc: Pekka Enberg Cc: Jacob Shin Link: http://lkml.kernel.org/r/1378519629-10433-1-git-send-email-yinghai@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/mm/init.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index 04664cd..ce32017 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -399,8 +399,25 @@ static unsigned long __init init_range_memory_mapping( return mapped_ram_size; } -/* (PUD_SHIFT-PMD_SHIFT)/2 */ -#define STEP_SIZE_SHIFT 5 +static unsigned long __init get_new_step_size(unsigned long step_size) +{ + /* + * Explain why we shift by 5 and why we don't have to worry about + * 'step_size << 5' overflowing: + * + * initial mapped size is PMD_SIZE (2M). + * We can not set step_size to be PUD_SIZE (1G) yet. + * In worse case, when we cross the 1G boundary, and + * PG_LEVEL_2M is not set, we will need 1+1+512 pages (2M + 8k) + * to map 1G range with PTE. Use 5 as shift for now. + * + * Don't need to worry about overflow, on 32bit, when step_size + * is 0, round_down() returns 0 for start, and that turns it + * into 0x100000000ULL. + */ + return step_size << 5; +} + void __init init_mem_mapping(void) { unsigned long end, real_end, start, last_start; @@ -449,7 +466,7 @@ void __init init_mem_mapping(void) min_pfn_mapped = last_start >> PAGE_SHIFT; /* only increase step_size after big range get mapped */ if (new_mapped_ram_size > mapped_ram_size) - step_size <<= STEP_SIZE_SHIFT; + step_size = get_new_step_size(step_size); mapped_ram_size += new_mapped_ram_size; }