From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758037AbcCaWiJ (ORCPT ); Thu, 31 Mar 2016 18:38:09 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36745 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752206AbcCaWiI (ORCPT ); Thu, 31 Mar 2016 18:38:08 -0400 Date: Thu, 31 Mar 2016 15:38:06 -0700 From: Andrew Morton To: Michal Hocko Cc: Chanho Min , Mel Gorman , Vlastimil Babka , David Rientjes , Dan Williams , Zhang Zhen , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gunho Lee Subject: Re: [PATCH] mm/highmem: simplify is_highmem() Message-Id: <20160331153806.960c2299698d40a625809e91@linux-foundation.org> In-Reply-To: <20160330092438.GG30729@dhcp22.suse.cz> References: <1459313022-11750-1-git-send-email-chanho.min@lge.com> <20160330092438.GG30729@dhcp22.suse.cz> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Mar 2016 11:24:38 +0200 Michal Hocko wrote: > On Wed 30-03-16 13:43:42, Chanho Min wrote: > > The is_highmem() is can be simplified by use of is_highmem_idx(). > > This patch removes redundant code and will make it easier to maintain > > if the zone policy is changed or a new zone is added. > > > > Signed-off-by: Chanho Min > > --- > > include/linux/mmzone.h | 5 +---- > > 1 file changed, 1 insertion(+), 4 deletions(-) > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index e23a9e7..9ac90c3 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -817,10 +817,7 @@ static inline int is_highmem_idx(enum zone_type idx) > > static inline int is_highmem(struct zone *zone) > > { > > #ifdef CONFIG_HIGHMEM > > - int zone_off = (char *)zone - (char *)zone->zone_pgdat->node_zones; > > - return zone_off == ZONE_HIGHMEM * sizeof(*zone) || > > - (zone_off == ZONE_MOVABLE * sizeof(*zone) && > > - zone_movable_is_highmem()); > > + return is_highmem_idx(zone_idx(zone)); > > This will reintroduce the pointer arithmetic removed by ddc81ed2c5d4 > ("remove sparse warning for mmzone.h") AFAICS. I have no idea how much > that matters though. The mentioned commit doesn't tell much about saves > except for > " > On X86_32 this saves a sar, but code size increases by one byte per > is_highmem() use due to 32-bit cmps rather than 16 bit cmps. > " The patch shrinks my i386 allmodconfig page_alloc.o by 50 bytes, and that has just two is_highmem() callsites. So I think it's OK from a code-size and performance piont of view