Re: [PATCH v1] mm/memory_hotplug: Easier calculation to get pages to next section boundary

[Wei Yang]

On Thu, Feb 06, 2020 at 07:19:45AM +0800, Wei Yang wrote:
>On Wed, Feb 05, 2020 at 02:52:51PM +0100, David Hildenbrand wrote:
>>Let's use a calculation that's easier to understand and calculates the
>>same result. Reusing existing macros makes this look nicer.
>>
>>We always want to have the number of pages (> 0) to the next section
>>boundary, starting from the current pfn.
>>
>>Suggested-by: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
>>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>>Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>>Cc: Oscar Salvador <osalvador@xxxxxxx>
>>Cc: Baoquan He <bhe@xxxxxxxxxx>
>>Cc: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
>>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
>Reviewed-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
>
>BTW, I got one question about hotplug size requirement.
>
>I thought the hotplug range should be section size aligned, while taking a
>look into current code function check_hotplug_memory_range() guard the range.
>
>This function says the range should be block_size aligned. And if I am
>correct, block size on x86 should be in the range
>
>    [MIN_MEMORY_BLOCK_SIZE, MEM_SIZE_FOR_LARGE_BLOCK]
>    
>And MIN_MEMORY_BLOCK_SIZE is section size.
>
>Seems currently we support subsection hotplug? Then how a subsection range got
>hotplug? Or this patch is a pre-requisite?
>

One more question is we support hot-add subsection memory but not support
hot-online subsection memory.

Is my understanding correct?

-- 
Wei Yang
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