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Subject: Re: [RFC v2 1/3] migrate: new struct migration and add it to struct
 page
To: Hui Zhu <zhuhui@xiaomi.com>, Minchan Kim <minchan@kernel.org>,
        Nitin Gupta <ngupta@vflare.org>,
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From: Vlastimil Babka <vbabka@suse.cz>
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Date: Thu, 15 Oct 2015 11:27:15 +0200
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On 10/15/2015 11:09 AM, Hui Zhu wrote:
> I got that add function interfaces is really not a good idea.
> So I add a new struct migration to put all migration interfaces and add
> this struct to struct page as union of "mapping".

That's better, but not as flexible as the previously proposed approaches 
that Sergey pointed you at:

  http://lkml.iu.edu/hypermail/linux/kernel/1507.0/03233.html
  http://lkml.iu.edu/hypermail/linux/kernel/1508.1/00696.html

There the operations are reachable via mapping, so we can support the 
special operations migration also when mapping is otherwise needed; your 
patch excludes mapping.