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

[Rik van Riel <riel@surriel.com>]

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On Fri, 2020-02-28 at 09:25 +0100, Vlastimil Babka wrote:
> On 2/28/20 2:21 AM, Rik van Riel wrote:
> > 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?
> 
> Oh right you are.
> 
> > 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.

-- 
All Rights Reversed.

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