Re: [PATCH v4 6/6] mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD

[David Hildenbrand]

On 15.03.24 11:55, Ryan Roberts wrote:
> On 15/03/2024 10:35, David Hildenbrand wrote:
> > > -        if (!pageout && pte_young(ptent)) {
> > > -            ptent = ptep_get_and_clear_full(mm, addr, pte,
> > > -                            tlb->fullmm);
> > > -            ptent = pte_mkold(ptent);
> > > -            set_pte_at(mm, addr, pte, ptent);
> > > -            tlb_remove_tlb_entry(tlb, pte, addr);
> > > +        if (!pageout) {
> > > +            for (; nr != 0; nr--, pte++, addr += PAGE_SIZE) {
> > > +                if (ptep_test_and_clear_young(vma, addr, pte))
> > > +                    tlb_remove_tlb_entry(tlb, pte, addr);
> > > +            }
> > >            }
> >
> >
> > The following might turn out a bit nicer: Make folio_pte_batch() collect
> > "any_young", then doing something like we do with "any_writable" in the fork()
> > case:
> >
> > ...
> >      nr = folio_pte_batch(folio, addr, pte, ptent, max_nr,
> >                   fpb_flags, NULL, any_young);
> >      if (any_young)
> >          pte_mkyoung(ptent)
> > ...
> >
> > if (!pageout && pte_young(ptent)) {
> >      mkold_full_ptes(mm, addr, pte, nr, tlb->fullmm);
> >      tlb_remove_tlb_entries(tlb, pte, nr, addr);
> > }
>
> I thought about that but decided that it would be better to only TLBI the actual
> entries that were young. Although looking at tlb_remove_tlb_entry() I see that
> it just maintains a range between the lowest and highest address, so this won't
> actually make any difference.

Yes, tlb_remove_tlb_entries() looks scarier than it actually is :)

--
Cheers,

David / dhildenb