From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx134.postini.com [74.125.245.134]) by kanga.kvack.org (Postfix) with SMTP id 981AD6B0044 for ; Thu, 23 Aug 2012 08:31:14 -0400 (EDT) Received: from /spool/local by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 23 Aug 2012 06:31:13 -0600 Received: from d03relay05.boulder.ibm.com (d03relay05.boulder.ibm.com [9.17.195.107]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 785A21FF003B for ; Thu, 23 Aug 2012 06:31:07 -0600 (MDT) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay05.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q7NCUjgV044412 for ; Thu, 23 Aug 2012 06:31:01 -0600 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q7NCUj9K002561 for ; Thu, 23 Aug 2012 06:30:45 -0600 Date: Thu, 23 Aug 2012 20:30:34 +0800 From: Gavin Shan Subject: Re: Fixup the page of buddy_higher address's calculation Message-ID: <20120823123034.GA3793@shangw.(null)> Reply-To: Gavin Shan References: <20120823095022.GB10685@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Li Haifeng Cc: Michal Hocko , Andrew Morton , Mel Gorman , Minchan Kim , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Aug 23, 2012 at 06:21:06PM +0800, Li Haifeng wrote: >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= pagea??s page address + (buddy - page)*sizeof(struct page) > >Clear? > It sounds reasonable. >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); Haifeng, Not sure it would be better? At least, the expression would be more explicitly meaningful than yours. higher_buddy = higher_page + (buddy_idx - combined_idx); Thanks, Gavin >> >> 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, send a message with 'unsubscribe linux-mm' in >the body to majordomo@kvack.org. For more info on Linux MM, >see: http://www.linux-mm.org/ . >Don't email: email@kvack.org > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org