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Subject: Re: [PATCH v3 6/9] mm, memory_hotplug: do not associate hotadded
 memory to zones until online
To: Michal Hocko <mhocko@kernel.org>,
        Dan Williams <dan.j.williams@gmail.com>
References: <20170410110351.12215-1-mhocko@kernel.org>
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 <20170410162547.GM4618@dhcp22.suse.cz>
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 <20170420090605.GD15781@dhcp22.suse.cz>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Andrea Arcangeli <aarcange@redhat.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Reza Arbab <arbab@linux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, qiuxishi@huawei.com,
        Kani Toshimitsu <toshi.kani@hpe.com>, slaoub@gmail.com,
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        Heiko Carstens <heiko.carstens@de.ibm.com>,
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        Martin Schwidefsky <schwidefsky@de.ibm.com>
From: Vlastimil Babka <vbabka@suse.cz>
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Date: Thu, 20 Apr 2017 12:51:42 +0200
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On 04/20/2017 11:06 AM, Michal Hocko wrote:
> On Thu 20-04-17 10:25:27, Vlastimil Babka wrote:
>>> + * intersection with the given zone
>>> + */
>>> +static inline bool zone_intersects(struct zone *zone,
>>> +		unsigned long start_pfn, unsigned long nr_pages)
>>> +{
>>
>> I'm looking at your current mmotm tree branch, which looks like this:
>>
>> + * Return true if [start_pfn, start_pfn + nr_pages) range has a non-mpty
>> + * intersection with the given zone
>> + */
>> +static inline bool zone_intersects(struct zone *zone,
>> +               unsigned long start_pfn, unsigned long nr_pages)
>> +{
>> +       if (zone_is_empty(zone))
>> +               return false;
>> +       if (zone->zone_start_pfn <= start_pfn && start_pfn < zone_end_pfn(zone))
>> +               return true;
>> +       if (start_pfn + nr_pages > zone->zone_start_pfn)
>> +               return true;
>>
>> A false positive is possible here, when start_pfn >= zone_end_pfn(zone)?
> 
> Ohh, right. Looks better?

Yeah.

You can add for the whole patch

Acked-by: Vlastimil Babka <vbabka@suse.cz>

But I can't guarantee some corner case won't surface. The hotplug code
is far from straightforward :(