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Wed, 5 Feb 2020 23:08:33 +0000 (UTC) Received: from localhost (ovpn-12-19.pek2.redhat.com [10.72.12.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ABEAA8DC12; Wed, 5 Feb 2020 23:08:29 +0000 (UTC) Date: Thu, 6 Feb 2020 07:08:26 +0800 From: Baoquan He To: Wei Yang Cc: David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, x86@kernel.org, Andrew Morton , Oscar Salvador , Michal Hocko , Pavel Tatashin , Dan Williams Subject: Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span() Message-ID: <20200205230826.GF8965@MiWiFi-R3L-srv> References: <20191006085646.5768-1-david@redhat.com> <20191006085646.5768-9-david@redhat.com> <20200205095924.GC24162@richard> <20200205144811.GF26758@MiWiFi-R3L-srv> <20200205225633.GA28446@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200205225633.GA28446@richard> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Archived-At: List-Archive: List-Post: On 02/06/20 at 06:56am, Wei Yang wrote: > On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote: > >Hi Wei Yang, > > > >On 02/05/20 at 05:59pm, Wei Yang wrote: > >> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > >> >index f294918f7211..8dafa1ba8d9f 100644 > >> >--- a/mm/memory_hotplug.c > >> >+++ b/mm/memory_hotplug.c > >> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, > >> > if (pfn) { > >> > zone->zone_start_pfn = pfn; > >> > zone->spanned_pages = zone_end_pfn - pfn; > >> >+ } else { > >> >+ zone->zone_start_pfn = 0; > >> >+ zone->spanned_pages = 0; > >> > } > >> > } else if (zone_end_pfn == end_pfn) { > >> > /* > >> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, > >> > start_pfn); > >> > if (pfn) > >> > zone->spanned_pages = pfn - zone_start_pfn + 1; > >> >+ else { > >> >+ zone->zone_start_pfn = 0; > >> >+ zone->spanned_pages = 0; > >> >+ } > >> > } > >> > >> If it is me, I would like to take out these two similar logic out. > > > >I also like this style. > >> > >> For example: > >> > >> if () { > >> } else if () { > >> } else { > >> goto out; > >Here the last else is unnecessary, right? > > > > I am afraid not. > > If the range is not the first or last, we would leave pfn not initialized. Ah, you are right. I forgot that one. Then pfn can be assigned the zone_start_pfn as the old code. Then the following logic is the same as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() have done the iteration the old for loop was doing. unsigned long pfn = zone_start_pfn; if () { } else if () { } /* The zone has no valid section */ if (!pfn) { zone->zone_start_pfn = 0; zone->spanned_pages = 0; }