From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx133.postini.com [74.125.245.133]) by kanga.kvack.org (Postfix) with SMTP id 19E9A6B0044 for ; Thu, 23 Aug 2012 06:21:09 -0400 (EDT) Received: by lahd3 with SMTP id d3so400755lah.14 for ; Thu, 23 Aug 2012 03:21:07 -0700 (PDT) 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 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Mel Gorman , Minchan Kim , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org 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_i= dx)). Maybe, a diagram is easier to understand. |-------------------------|-------------| page combined buddy buddy's page address=3D page=91s page address + (buddy - page)*sizeof(struc= t 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 th= e > 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 =3D buddy_idx & page_idx; >> higher_page =3D page + (combined_idx - page_idx); >> buddy_idx =3D __find_buddy_index(combined_idx, order + 1= ); >> - higher_buddy =3D page + (buddy_idx - combined_idx); >> + higher_buddy =3D 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[migrat= etype]); >> -- >> 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