From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760431Ab3HOGDm (ORCPT ); Thu, 15 Aug 2013 02:03:42 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:41770 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752359Ab3HOGDj (ORCPT ); Thu, 15 Aug 2013 02:03:39 -0400 From: Yinghai Lu To: "H. Peter Anvin" Cc: Ingo Molnar , Pekka Enberg , Jacob Shin , linux-kernel@vger.kernel.org, Yinghai Lu Subject: [PATCH] x86, mm: Add comments for step_size shift Date: Wed, 14 Aug 2013 23:03:36 -0700 Message-Id: <1376546616-17489-1-git-send-email-yinghai@kernel.org> X-Mailer: git-send-email 1.8.1.4 X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As request by hpa, add comments for why we choose 5 for step size shift. Signed-off-by: Yinghai Lu Reviewed-by: Tang Chen Tested-by: Tang Chen --- arch/x86/mm/init.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) Index: linux-2.6/arch/x86/mm/init.c =================================================================== --- linux-2.6.orig/arch/x86/mm/init.c +++ linux-2.6/arch/x86/mm/init.c @@ -395,8 +395,23 @@ static unsigned long __init init_range_m 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; }