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

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Date:   Thu, 27 Feb 2020 20:21:38 -0500
From:   Rik van Riel <riel@...riel.com>
To:     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, vbabka@...e.cz, 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 Thu, 2020-02-27 at 15:41 -0800, Mike Kravetz wrote:
> On 2/27/20 1:32 PM, Rik van Riel wrote:
> > 
> > +++ b/mm/page_alloc.c
> > @@ -8253,14 +8253,19 @@ struct page *has_unmovable_pages(struct
> > zone *zone, struct page *page,
> >  
> >  		/*
> >  		 * Hugepages are not in LRU lists, but they're movable.
> > +		 * THPs are on the LRU, but need to be counted as
> > #small pages.
> >  		 * We need not scan over tail pages because we don't
> >  		 * handle each tail page individually in migration.
> >  		 */
> > -		if (PageHuge(page)) {
> > +		if (PageHuge(page) || PageTransCompound(page)) {
> >  			struct page *head = compound_head(page);
> >  			unsigned int skip_pages;
> >  
> > -			if
> > (!hugepage_migration_supported(page_hstate(head)))
> > +			if (PageHuge(page) &&
> > +			    !hugepage_migration_supported(page_hstate(h
> > ead)))
> > +				return page;
> > +
> > +			if (!PageLRU(head) && !__PageMovable(head))
> 
> Pretty sure this is going to be true for hugetlb pages.  So, this
> will change
> behavior and make all hugetlb pages look unmovable.  Perhaps, only
> check this
> condition for THP pages?

Does that need to be the following, then?

     if (PageTransHuge(head) && !PageHuge(page) && !PageLRU(head) &&
!__PageMovable(head))
                 return page;

That's an easy one liner I would be happy to send in
if everybody agrees that should fix things :)

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