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Date:   Wed, 5 Feb 2020 21:34:42 +0800
From:   Baoquan He <bhe@redhat.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     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 <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Wei Yang <richardw.yang@linux.intel.com>
Subject: Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes"
 in shrink_zone_span()
Message-ID: <20200205133442.GC8965@MiWiFi-R3L-srv>
References: <20191006085646.5768-1-david@redhat.com>
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 <20200204142516.GD26758@MiWiFi-R3L-srv>
 <e0006cc4-d448-89c6-38c0-51da7fc08715@redhat.com>
 <20200205124329.GE26758@MiWiFi-R3L-srv>
 <cd353848-301a-025d-dd66-44d76e1bbc44@redhat.com>
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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 <akpm@linux-foundation.org>
> >>>> Cc: Oscar Salvador <osalvador@suse.de>
> >>>> Cc: Michal Hocko <mhocko@suse.com>
> >>>> Cc: David Hildenbrand <david@redhat.com>
> >>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> >>>> Cc: Dan Williams <dan.j.williams@intel.com>
> >>>> Cc: Wei Yang <richardw.yang@linux.intel.com>
> >>>> Signed-off-by: David Hildenbrand <david@redhat.com>
> >>>> ---
> >>>>  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. 

> 
> 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.