On 06.02.20 10:35, Baoquan He wrote:
> On 02/06/20 at 09:50am, David Hildenbrand wrote:
>> On 06.02.20 06:39, Baoquan He wrote:
>>> In commit 950b68d9178b ("mm/memory_hotplug: don't check for "all holes"
>>> in shrink_zone_span()"), the zone->zone_start_pfn/->spanned_pages
>>> resetting is moved into the if()/else if() branches, if the zone becomes
>>> empty. However the 2nd resetting code block may cause misunderstanding.
>>>
>>> So take the resetting codes out of the conditional checking and handling
>>> branches just as the old code does, the find_smallest_section_pfn()and
>>> find_biggest_section_pfn() searching have done the the same thing as
>>> the old for loop did, the logic is kept the same as the old code. This
>>> can remove the possible confusion.
>>>
>>> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
>>> ---
>>> mm/memory_hotplug.c | 14 ++++++--------
>>> 1 file changed, 6 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 089b6c826a9e..475d0d68a32c 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -398,7 +398,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
>>> static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>> unsigned long end_pfn)
>>> {
>>> - unsigned long pfn;
>>> + unsigned long pfn = zone->zone_start_pfn;
>>> int nid = zone_to_nid(zone);
>>>
>>> zone_span_writelock(zone);
>>> @@ -414,9 +414,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>> if (pfn) {
>>> zone->spanned_pages = zone_end_pfn(zone) - pfn;
>>> zone->zone_start_pfn = pfn;
>>> - } else {
>>> - zone->zone_start_pfn = 0;
>>> - zone->spanned_pages = 0;
>>> }
>>> } else if (zone_end_pfn(zone) == end_pfn) {
>>> /*
>>> @@ -429,10 +426,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>> start_pfn);
>>> if (pfn)
>>> zone->spanned_pages = pfn - zone->zone_start_pfn + 1;
>>> - else {
>>> - zone->zone_start_pfn = 0;
>>> - zone->spanned_pages = 0;
>>> - }
>>> + }
>>> +
>>> + if (!pfn) {
>>> + zone->zone_start_pfn = 0;
>>> + zone->spanned_pages = 0;
>>> }
>>> zone_span_writeunlock(zone);
>>> }
>>>
>>
>> So, what if your zone starts at pfn 0? Unlikely that we can actually
>> offline that, but still it is more confusing than the old code IMHO.
>> Then I prefer to drop the second else case as discussed instead.
>
> Hmm, pfn is initialized as zone->zone_start_pfn, does it matter?
> The impossible empty zone won't go wrong if it really happen.
>
If you offline any memory block that belongs to the lowest zone
(zone->zone_start_pfn == 0) but does not fall on a boundary (so that you
can actually shrink), you would mark the whole zone offline. That's
broken unless I am missing something.
--
Thanks,
David / dhildenb
