From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934591AbbI2KaE (ORCPT ); Tue, 29 Sep 2015 06:30:04 -0400 Received: from mail-wi0-f193.google.com ([209.85.212.193]:33927 "EHLO mail-wi0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933838AbbI2K34 (ORCPT ); Tue, 29 Sep 2015 06:29:56 -0400 Date: Tue, 29 Sep 2015 13:26:57 +0300 From: Alexandru Moise <00moses.alexander00@gmail.com> To: Mel Gorman Cc: akpm@linux-foundation.org, mgorman@suse.dec, vbabka@suse.cz, mhocko@suse.com, js1304@gmail.com, hannes@cmpxchg.org, alexander.h.duyck@redhat.com, sasha.levin@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: change free_cma and free_pages declarations to unsigned Message-ID: <20150929102657.GA27621@gmail.com> References: <20150927210416.GA20144@gmail.com> <20150929101327.GW25655@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150929101327.GW25655@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 29, 2015 at 11:13:27AM +0100, Mel Gorman wrote: > On Sun, Sep 27, 2015 at 09:04:16PM +0000, Alexandru Moise wrote: > > Their stored values come from zone_page_state() which returns > > an unsigned long. To improve code correctness we should avoid > > mixing signed and unsigned integers. > > > > Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com> > > --- > > mm/page_alloc.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 48aaf7b..f55e3a2 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -2242,7 +2242,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order, > > /* free_pages may go negative - that's OK */ > > long min = mark; > > int o; > > - long free_cma = 0; > > + unsigned long free_cma = 0; > > > > NAK. > > free_cma is used with free_pages which is explicitly commented as saying > it can go negative. With your patch, there is a signed/unsigned operation > where the unsigned type cannot fit into the signed type which casts them > both to unsigned which is then broken for the comparison. This patch > looks broken for very subtle reasons. Please do not do any similar style > patches to this because they can introduce subtle breakage if issues are > not caught at review. > Understood, I thought the comment only applied to the "min" variable.