Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933075Ab2HWKVY (ORCPT ); Thu, 23 Aug 2012 06:21:24 -0400 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:57883 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932542Ab2HWKVI convert rfc822-to-8bit (ORCPT ); Thu, 23 Aug 2012 06:21:08 -0400 MIME-Version: 1.0 In-Reply-To: <20120823095022.GB10685@dhcp22.suse.cz> References: <20120823095022.GB10685@dhcp22.suse.cz> Date: Thu, 23 Aug 2012 18:21:06 +0800 Message-ID: Subject: Re: Fixup the page of buddy_higher address's calculation From: Li Haifeng To: Michal Hocko Cc: Andrew Morton , Mel Gorman , Minchan Kim , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2316 Lines: 64 I am sorry for my mistake. higher_buddy is corresponding with buddy_index, and higher page is corresponding with combined_idx. That is right. But, How we get the page address from index offset? The key answer is what is the base value. So calculating the address based page should be (page + (buddy_idx - page_idx)). Maybe, a diagram is easier to understand. |-------------------------|-------------| page combined buddy buddy's page address= page?s page address + (buddy - page)*sizeof(struct page) Clear? 2012/8/23 Michal Hocko : > On Thu 23-08-12 16:40:13, Li Haifeng wrote: >> From d7cd78f9d71a5c9ddeed02724558096f0bb4508a Mon Sep 17 00:00:00 2001 >> From: Haifeng Li >> Date: Thu, 23 Aug 2012 16:27:19 +0800 >> Subject: [PATCH] Fixup the page of buddy_higher address's calculation > > Some general questions: > Any word about the change? Is it really that obvious? Why do you think the > current state is incorrect? How did you find out? > > And more specific below: > >> Signed-off-by: Haifeng Li >> --- >> mm/page_alloc.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index ddbc17d..5588f68 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -579,7 +579,7 @@ static inline void __free_one_page(struct page *page, >> combined_idx = buddy_idx & page_idx; >> higher_page = page + (combined_idx - page_idx); >> buddy_idx = __find_buddy_index(combined_idx, order + 1); >> - higher_buddy = page + (buddy_idx - combined_idx); >> + higher_buddy = page + (buddy_idx - page_idx); > > We are finding buddy index for combined_idx so why should we use > page_idx here? > >> if (page_is_buddy(higher_page, higher_buddy, order + 1)) { >> list_add_tail(&page->lru, >> &zone->free_area[order].free_list[migratetype]); >> -- >> 1.7.5.4 > > -- > Michal Hocko > SUSE Labs -- 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/