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Subject: Re: [PATCH v2 2/2] mm,thp,compaction,cma: allow THP migration for CMA
 allocations
To:     Rik van Riel <riel@surriel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        linux-kernel@vger.kernel.org
Cc:     kernel-team@fb.com, akpm@linux-foundation.org, linux-mm@kvack.org,
        mhocko@kernel.org, mgorman@techsingularity.net,
        rientjes@google.com, aarcange@redhat.com, ziy@nvidia.com
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Date:   Fri, 28 Feb 2020 15:39:38 +0100
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On 2/28/20 3:32 PM, Rik van Riel wrote:

>>> Does that need to be the following, then?
>>>
>>>      if (PageTransHuge(head) && !PageHuge(page) && !PageLRU(head)
>>> &&
>>> !__PageMovable(head))
>>>                  return page;
>>
>> I would instead make it an "else if" to the "if (PageHuge(page)...)"
>> above.
> 
> That was my first thought too, but that could break on
> pages that are PageHuge when hugepage_migration_supported
> returns true.

Right, so then

if (PageHuge()) {
	if (!migration_supported) return false;
} else if (!PageLRU(head) ...) {
   etc...

IMHO it's better than adding more tests to the second if.