From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758714Ab3FMNlJ (ORCPT ); Thu, 13 Jun 2013 09:41:09 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:8481 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1757099Ab3FMN15 (ORCPT ); Thu, 13 Jun 2013 09:27:57 -0400 X-IronPort-AV: E=Sophos;i="4.87,858,1363104000"; d="scan'208";a="7537675" From: Tang Chen To: tglx@linutronix.de, mingo@elte.hu, hpa@zytor.com, akpm@linux-foundation.org, tj@kernel.org, trenn@suse.de, yinghai@kernel.org, jiang.liu@huawei.com, wency@cn.fujitsu.com, laijs@cn.fujitsu.com, isimatu.yasuaki@jp.fujitsu.com, mgorman@suse.de, minchan@kernel.org, mina86@mina86.com, gong.chen@linux.intel.com, vasilis.liaskovitis@profitbricks.com, lwoodman@redhat.com, riel@redhat.com, jweiner@redhat.com, prarit@redhat.com Cc: x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [Part1 PATCH v5 20/22] x86, mm: Add comments for step_size shift Date: Thu, 13 Jun 2013 21:03:07 +0800 Message-Id: <1371128589-8953-21-git-send-email-tangchen@cn.fujitsu.com> X-Mailer: git-send-email 1.7.10.1 In-Reply-To: <1371128589-8953-1-git-send-email-tangchen@cn.fujitsu.com> References: <1371128589-8953-1-git-send-email-tangchen@cn.fujitsu.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2013/06/13 20:58:18, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2013/06/13 20:58:28, Serialize complete at 2013/06/13 20:58:28 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yinghai Lu As requested by hpa, add comments for why we choose 5 to be the step size shift. Signed-off-by: Yinghai Lu Reviewed-by: Tang Chen Tested-by: Tang Chen --- arch/x86/mm/init.c | 21 ++++++++++++++++++--- 1 files changed, 18 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index 3c21f16..5f38e72 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -395,8 +395,23 @@ 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) +{ + /* + * initial mapped size is PMD_SIZE, aka 2M. + * We can not set step_size to be PUD_SIZE aka 1G yet. + * In worse case, when 1G is cross the 1G boundary, and + * PG_LEVEL_2M is not set, we will need 1+1+512 pages (aka 2M + 8k) + * to map 1G range with PTE. Use 5 as shift for now. + */ + unsigned long new_step_size = step_size << 5; + + if (new_step_size > step_size) + step_size = new_step_size; + + return step_size; +} + void __init init_mem_mapping(void) { unsigned long end, real_end, start, last_start; @@ -445,7 +460,7 @@ 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; } -- 1.7.1