Re: [PATCH 2/2] mm/khugepaged: Convert release_pte_pages() to use folios

[Alexandre Ghiti]

Hi Matthew,

On 2/13/23 16:50, Matthew Wilcox wrote:
> On Mon, Feb 13, 2023 at 04:28:05PM +0100, Alexandre Ghiti wrote:
> > The issue lies here: before using pteval in pfn_folio(), we should test it.
> > The following patch fixes the issue for me:
> Thanks for debugging it.  I'd rather see this written as ...
>
> 		pte_t pteval = *_pte;
> +		unsigned long pfn;
>
> +		if (pte_none(pteval))
> +			continue;
> +		pfn = pte_pfn(pteval);
> +		if (is_zero_pfn(pfn))
> +			continue;
> +		folio = pfn_folio(pfn);
> +		if (folio_test_large(folio))
> +			continue;
> 		release_pte_folio(folio);
>
> makes sense?


Sure, that's fine by me, I can send that or I'll add my tested-by on 
what you send, whatever suits you.

Alex


> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index eb38bd1b1b2f..fef3414b481b 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -514,10 +514,12 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
> >          while (--_pte >= pte) {
> >                  pte_t pteval = *_pte;
> >
> > -               folio = pfn_folio(pte_pfn(pteval));
> > -               if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
> > -                               !folio_test_large(folio))
> > -                       release_pte_folio(folio);
> > +               if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval))) {
> > +                       folio = pfn_folio(pte_pfn(pteval));
> > +
> > +                       if (!folio_test_large(folio))
> > +                               release_pte_folio(folio);
> > +               }
> >          }
> >
> >          list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
> >
> >
> > @Marek: could you give it a try?
> >
> > I can send a separate patch if needed, let me know.
> >
> > Thanks,
> >
> > Alex
> >
> >
> > > >     		if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
> > > > -				!PageCompound(page))
> > > > -			release_pte_page(page);
> > > > +				!folio_test_large(folio))
> > > > +			release_pte_folio(folio);
> > > >     	}
> > > > -	list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
> > > > -		list_del(&page->lru);
> > > > -		release_pte_page(page);
> > > > +	list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
> > > > +		list_del(&folio->lru);
> > > > +		release_pte_folio(folio);
> > > >     	}
> > > >     }
> > > Best regards