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

[Kirill A. Shutemov]

On Thu, Jun 02, 2016 at 12:47:57PM -0700, Hugh Dickins wrote:
> 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?

Hm. I thought I had a reason for not using page's refcount, but I can't
find any now. We would loose sanity check in put_huge_zero_page(), but I
guess it's fine since we never triggered it.

I'll put it to my todo list.

-- 
 Kirill A. Shutemov