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Subject: Re: [PATCH v2 4/5] mm/memory_hotplug: Make sure the pfn is aligned to
 the order when onlining
To:     Michal Hocko <mhocko@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Arun KS <arunks@codeaurora.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Dan Williams <dan.j.williams@intel.com>
References: <20190814154109.3448-1-david@redhat.com>
 <20190814154109.3448-5-david@redhat.com>
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From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <80fe203b-f598-0296-7b8f-16d0e3e6a98a@redhat.com>
Date:   Wed, 14 Aug 2019 21:04:16 +0200
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On 14.08.19 20:32, Michal Hocko wrote:
> On Wed 14-08-19 18:09:16, David Hildenbrand wrote:
>> On 14.08.19 17:41, David Hildenbrand wrote:
>>> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
>>> order") assumed that any PFN we get via memory resources is aligned to
>>> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
>>> check the alignment and fallback to single pages.
>>>
>>> Cc: Arun KS <arunks@codeaurora.org>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Oscar Salvador <osalvador@suse.de>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>  mm/memory_hotplug.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 63b1775f7cf8..f245fb50ba7f 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>>>  	 */
>>>  	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
>>>  		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
>>> +		/* __free_pages_core() wants pfns to be aligned to the order */
>>> +		if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
>>> +			order = 0;
>>>  		(*online_page_callback)(pfn_to_page(pfn), order);
>>>  	}
>>>  
>>>
>>
>> @Michal, if you insist, we can drop this patch. "break first and fix
>> later" is not part of my DNA :)
> 
> I do not insist but have already expressed that I am not a fan of this
> change. Also I think that "break first" is quite an over statement here.
> 

Well this version is certainly nicer than the previous one. I'll let
Andrew decide if he wants to pick it up or drop it from this series.

Thanks!

-- 

Thanks,

David / dhildenb