linux-kernel - Re: [PATCH v2 2/2] mm,thp,compaction,cma: allow THP migration for CMA allocations

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Date:   Fri, 28 Feb 2020 15:39:38 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Rik van Riel <riel@...riel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        linux-kernel@...r.kernel.org
Cc:     kernel-team@...com, akpm@...ux-foundation.org, linux-mm@...ck.org,
        mhocko@...nel.org, mgorman@...hsingularity.net,
        rientjes@...gle.com, aarcange@...hat.com, ziy@...dia.com
Subject: Re: [PATCH v2 2/2] mm,thp,compaction,cma: allow THP migration for CMA
 allocations

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.