Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753829Ab3FOA6v (ORCPT ); Fri, 14 Jun 2013 20:58:51 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:47618 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753521Ab3FOA5G (ORCPT ); Fri, 14 Jun 2013 20:57:06 -0400 From: Yinghai Lu To: "H. Peter Anvin" Cc: Thomas Gleixner , Ingo Molnar , Andrew Morton , Tejun Heo , Thomas Renninger , Tang Chen , linux-kernel@vger.kernel.org, Yinghai Lu Subject: [PATCH v5 20/22] x86, mm: Add comments for step_size shift Date: Fri, 14 Jun 2013 17:56:38 -0700 Message-Id: <1371257800-11720-21-git-send-email-yinghai@kernel.org> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1371257800-11720-1-git-send-email-yinghai@kernel.org> References: <1371257800-11720-1-git-send-email-yinghai@kernel.org> X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1814 Lines: 57 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(-) 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; } -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/