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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()
Date: Wed, 5 Feb 2020 22:12:54 +0800
Message-ID: <20200205141254.GD8965@MiWiFi-R3L-srv> (raw)
In-Reply-To: <2868343a-745b-e2b6-7e78-d5649c00ee31@redhat.com>

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 <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. 
> 
> 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.



  reply index

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-06  8:56 [PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages() David Hildenbrand
2019-10-06 19:58   ` Damian Tometzki
2019-10-06 20:13     ` David Hildenbrand
2019-10-14  9:05   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 02/10] mm/memmap_init: Update variable name in memmap_init_zone David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 03/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_pgdat_span() David Hildenbrand
2019-10-14  9:31   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span() David Hildenbrand
2019-10-14  9:32   ` David Hildenbrand
2019-10-14 19:17     ` Andrew Morton
2019-11-19 14:16       ` David Hildenbrand
2019-11-19 20:44         ` Andrew Morton
2019-10-06  8:56 ` [PATCH v6 05/10] mm/memory_hotplug: Shrink zones when offlining memory David Hildenbrand
2019-10-14  9:39   ` David Hildenbrand
2019-10-14 19:16     ` Andrew Morton
2019-10-27 22:45   ` David Hildenbrand
2019-11-30 23:21     ` Andrew Morton
2019-11-30 23:43       ` David Hildenbrand
2019-12-18 17:08       ` David Hildenbrand
2019-12-18 20:16         ` Andrew Morton
2019-12-03 15:10   ` Oscar Salvador
2019-12-03 15:27     ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 06/10] mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone() David Hildenbrand
2019-10-16 14:01   ` David Hildenbrand
2020-02-04  8:59   ` Oscar Salvador
2019-10-06  8:56 ` [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn David Hildenbrand
2020-02-04  9:06   ` Oscar Salvador
2020-02-05  8:57   ` Wei Yang
2020-02-05  8:59     ` David Hildenbrand
2020-02-05  9:26       ` Wei Yang
2019-10-06  8:56 ` [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span() David Hildenbrand
2020-02-04  9:13   ` Oscar Salvador
2020-02-04  9:20     ` David Hildenbrand
2020-02-04 14:25   ` Baoquan He
2020-02-04 14:42     ` David Hildenbrand
2020-02-05 12:43       ` Baoquan He
2020-02-05 13:20         ` David Hildenbrand
2020-02-05 13:34           ` Baoquan He
2020-02-05 13:38             ` David Hildenbrand
2020-02-05 14:12               ` Baoquan He [this message]
2020-02-05 14:16                 ` David Hildenbrand
2020-02-05 14:26                   ` Baoquan He
2020-02-05  9:59   ` Wei Yang
2020-02-05 14:48     ` Baoquan He
2020-02-05 22:56       ` Wei Yang
2020-02-05 23:08         ` Baoquan He
2020-02-05 23:26           ` Wei Yang
2020-02-05 23:30             ` Baoquan He
2020-02-05 23:34               ` Wei Yang
2020-02-05 14:54     ` David Laight
2020-02-05 14:55       ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 09/10] mm/memory_hotplug: Drop local variables " David Hildenbrand
2020-02-04  9:26   ` Oscar Salvador
2020-02-04  9:29     ` David Hildenbrand
2020-02-05 10:07   ` Wei Yang
2019-10-06  8:56 ` [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages() David Hildenbrand
2020-02-04  9:46   ` Oscar Salvador
2020-02-04 12:41     ` David Hildenbrand
2020-02-04 13:13       ` Segher Boessenkool
2020-02-04 13:38         ` David Hildenbrand
2020-02-05 12:51           ` Segher Boessenkool
2020-02-05 13:17             ` David Hildenbrand
2020-02-05 13:18               ` David Hildenbrand
2020-02-05 13:23                 ` David Hildenbrand
2020-02-05 11:48   ` Wei Yang
2019-12-02  9:09 ` [PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory David Hildenbrand
2019-12-03 13:36   ` Oscar Salvador
2020-01-31  4:40     ` Andrew Morton
2020-01-31  9:18       ` David Hildenbrand
2020-01-31 10:03         ` Michal Hocko
2020-01-31 10:36           ` David Hildenbrand
2020-02-04  1:46         ` Andrew Morton
2020-02-04  8:45           ` David Hildenbrand
2020-02-04  9:51             ` Oscar Salvador

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