Re: [PATCH v2] mm: huge_memory: convert split_huge_pages_all() to use a folio

[Kefeng Wang]

On 2022/12/31 5:45, Andrew Morton wrote:
> On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
> > Straightforwardly convert split_huge_pages_all() to use a folio.
> >
> > ...
> >
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2932,6 +2932,7 @@ static void split_huge_pages_all(void)
> >   {
> >   	struct zone *zone;
> >   	struct page *page;
> > +	struct folio *folio;
> >   	unsigned long pfn, max_zone_pfn;
> >   	unsigned long total = 0, split = 0;
> >   
> > @@ -2944,24 +2945,32 @@ static void split_huge_pages_all(void)
> >   			int nr_pages;
> >   
> >   			page = pfn_to_online_page(pfn);
> > -			if (!page || !get_page_unless_zero(page))
> > +			if (!page || PageTail(page))
> > +				continue;
> > +			folio = page_folio(page);
> > +			if (!folio_try_get(folio))
> >   				continue;
> >   
> > -			if (zone != page_zone(page))
> > +			if (unlikely(page_folio(page) != folio))
> > +				goto next;
> > +
> > +			if (zone != folio_zone(folio))
> >   				goto next;
>
> I'm still not understanding the above hunk.  Why is the
> "page_folio(page) != folio" check added?  Should it be commented?

There is a comment in try_get_folio(), is it enough?