Re: [BUG/REGRESSION] THP: broken page count after commit aa88b68c

[Hugh Dickins]

On Thu, 2 Jun 2016, Kirill A. Shutemov wrote:
> On Thu, Jun 02, 2016 at 05:21:41PM +0200, Gerald Schaefer wrote:
> > 
> > The following quick hack fixed the issue:
> > 
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index 0d457e7..c99463a 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -252,7 +252,10 @@ static inline void free_swap_cache(struct page *page)
> >  void free_page_and_swap_cache(struct page *page)
> >  {
> >  	free_swap_cache(page);
> > -	put_page(page);
> > +	if (is_huge_zero_page(page))
> > +		put_huge_zero_page();
> > +	else
> > +		put_page(page);
> >  }
> >  
> >  /*
> 
> The fix looks good to me.

Is there a good reason why the refcount of the huge_zero_page is
huge_zero_refcount, instead of the refcount of the huge_zero_page?
Wouldn't the latter avoid such is_huge_zero_page() special-casing?

Hugh