From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 1F9AB6B002D for ; Tue, 15 Nov 2011 08:24:14 -0500 (EST) Date: Tue, 15 Nov 2011 14:24:09 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c Message-ID: <20111115132409.GA7551@tiehlicka.suse.cz> References: <4EC21D78.4080508@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4EC21D78.4080508@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wang Sheng-Hui Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue 15-11-11 16:06:16, Wang Sheng-Hui wrote: > Per the void prep_compound_page(struct page *page, unsigned long order) code, > compound pages use PG_head/PG_tail, This is true only for CONFIG_PAGEFLAGS_EXTENDED otherwise we trick it by PG_compound & ~PG_reclaim = head page PG_compound & PG_reclaim = tail page Have a look at PG_head_tail_mask > and only tail pages point at head page using their ->first_page field. This part is correct. > > Signed-off-by: Wang Sheng-Hui > --- > mm/page_alloc.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6e8ecb6..f645ce8 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -332,8 +332,8 @@ out: > * > * The remaining PAGE_SIZE pages are called "tail pages". > * > - * All pages have PG_compound set. All pages have their ->private pointing at > - * the head page (even the head page has this). > + * Head page has PG_head set, and all tail pages have PG_tail set. All tail > + * pages have their ->first_page pointing at the head page. > * > * The first tail page's ->lru.next holds the address of the compound page's > * put_page() function. Its ->lru.prev holds the order of allocation. > -- > 1.7.1 > > -- > 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/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: email@kvack.org -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org