From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id B59CA6B0038 for ; Sun, 19 Mar 2017 10:30:18 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id n11so11970443wma.5 for ; Sun, 19 Mar 2017 07:30:18 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 5si19161028wrb.21.2017.03.19.07.30.17 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sun, 19 Mar 2017 07:30:17 -0700 (PDT) Date: Sun, 19 Mar 2017 10:30:13 -0400 From: Michal Hocko Subject: Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags Message-ID: <20170319143012.GB12414@dhcp22.suse.cz> References: <20170318003914.24839-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170318003914.24839-1-richard.weiyang@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Sat 18-03-17 08:39:14, Wei Yang wrote: > The field page->flags is defined as unsigned long and is divided into > several parts to store different information of the page, like section, > node, zone. Which means all parts must sit in the one "unsigned > long". > > BITS_PER_LONG is used in several places to ensure this applies. > > #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS > #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS > #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS > > While we use "sizeof(unsigned long) * 8" in the definition of > SECTIONS_PGOFF > > #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH) > > This may not be that obvious for audience to catch the point. > > This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to > make all this consistent. I am not really sure this is an improvement. page::flags is unsigned long nad the current code reflects that type. > Signed-off-by: Wei Yang > --- > include/linux/mm.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index b84615b0f64c..a5d80de089ff 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -684,7 +684,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf); > */ > > /* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_CPUPID] | ... | FLAGS | */ > -#define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH) > +#define SECTIONS_PGOFF (BITS_PER_LONG - SECTIONS_WIDTH) > #define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH) > #define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH) > #define LAST_CPUPID_PGOFF (ZONES_PGOFF - LAST_CPUPID_WIDTH) > -- > 2.11.0 > -- 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