linux-kernel - Re: [PATCH 2/2] mm/khugepaged: Convert release_pte

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Date:   Mon, 13 Feb 2023 12:38:56 -0800
From:   Vishal Moola <vishal.moola@...il.com>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 2/2] mm/khugepaged: Convert release_pte_pages() to use folios

On Mon, Feb 13, 2023 at 7:55 AM Alexandre Ghiti <alex@...ti.fr> wrote:
>
> 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.

Thanks for debugging this! I'll send a fix patch using Matthew's
approach later today.

> 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