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Wed, 5 Feb 2020 14:13:00 +0000 (UTC) Received: from localhost (ovpn-12-97.pek2.redhat.com [10.72.12.97]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DEB9686C4A; Wed, 5 Feb 2020 14:12:57 +0000 (UTC) Date: Wed, 5 Feb 2020 22:12:54 +0800 From: Baoquan He To: David Hildenbrand Subject: Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span() Message-ID: <20200205141254.GD8965@MiWiFi-R3L-srv> References: <20191006085646.5768-1-david@redhat.com> <20191006085646.5768-9-david@redhat.com> <20200204142516.GD26758@MiWiFi-R3L-srv> <20200205124329.GE26758@MiWiFi-R3L-srv> <20200205133442.GC8965@MiWiFi-R3L-srv> <2868343a-745b-e2b6-7e78-d5649c00ee31@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2868343a-745b-e2b6-7e78-d5649c00ee31@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-s390@vger.kernel.org, Michal Hocko , linux-ia64@vger.kernel.org, Pavel Tatashin , linux-sh@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Wei Yang , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Dan Williams , linux-arm-kernel@lists.infradead.org, Oscar Salvador Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 02/05/20 at 02:38pm, David Hildenbrand wrote: > On 05.02.20 14:34, Baoquan He wrote: > > On 02/05/20 at 02:20pm, David Hildenbrand wrote: > >> On 05.02.20 13:43, Baoquan He wrote: > >>> On 02/04/20 at 03:42pm, David Hildenbrand wrote: > >>>> On 04.02.20 15:25, Baoquan He wrote: > >>>>> On 10/06/19 at 10:56am, David Hildenbrand wrote: > >>>>>> If we have holes, the holes will automatically get detected and removed > >>>>>> once we remove the next bigger/smaller section. The extra checks can > >>>>>> go. > >>>>>> > >>>>>> Cc: Andrew Morton > >>>>>> Cc: Oscar Salvador > >>>>>> Cc: Michal Hocko > >>>>>> Cc: David Hildenbrand > >>>>>> Cc: Pavel Tatashin > >>>>>> Cc: Dan Williams > >>>>>> Cc: Wei Yang > >>>>>> Signed-off-by: David Hildenbrand > >>>>>> --- > >>>>>> mm/memory_hotplug.c | 34 +++++++--------------------------- > >>>>>> 1 file changed, 7 insertions(+), 27 deletions(-) > >>>>>> > >>>>>> 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; > >>>>> > >>>>> Thinking in which case (zone_start_pfn != start_pfn) and it comes here. > >>>> > >>>> Could only happen in case the zone_start_pfn would have been "out of the > >>>> zone already". If you ask me: unlikely :) > >>> > >>> Yeah, I also think it's unlikely to come here. > >>> > >>> The 'if (zone_start_pfn == start_pfn)' checking also covers the case > >>> (zone_start_pfn == start_pfn && zone_end_pfn == end_pfn). So this > >>> zone_start_pfn/spanned_pages resetting can be removed to avoid > >>> confusion. > >> > >> At least I would find it more confusing without it (or want a comment > >> explaining why this does not have to be handled and why the !pfn case is > >> not possible). > > > > I don't get why being w/o it will be more confusing, but it's OK since > > it doesn't impact anything. > > Because we could actually BUG_ON(!pfn) here, right? Only having a "if > (pfn)" leaves the reader wondering "why is the other case not handled". > > > > >> > >> Anyhow, that patch is already upstream and I don't consider this high > >> priority. Thanks :) > > > > Yeah, noticed you told Wei the status in another patch thread, I am fine > > with it, just leave it to you to decide. Thanks. > > I am fairly busy right now. Can you send a patch (double-checking and > making this eventually unconditional?). Thanks! Understood, sorry about the noise, David. I will think about this.