Re: [PATCH v3 4/9] mm: introduce skip_none_ptes()

[Qi Zheng]

On 2024/11/15 18:22, David Hildenbrand wrote:
> > > > *nr_skip = nr;
> > > >
> > > > and then:
> > > >
> > > > zap_pte_range
> > > > --> nr = do_zap_pte_range(tlb, vma, pte, addr, end, details, &skip_nr,
> > > >                           rss, &force_flush, &force_break);
> > > >        if (can_reclaim_pt) {
> > > >            none_nr += count_pte_none(pte, nr);
> > > >            none_nr += nr_skip;
> > > >        }
> > > >
> > > > Right?
> > >
> > > Yes. I did not look closely at the patch that adds the counting of
> >
> > Got it.
> >
> > > pte_none though (to digest why it is required :) ).
> >
> > Because 'none_nr == PTRS_PER_PTE' is used in patch #7 to detect
> > empty PTE page.
>
> Okay, so the problem is that "nr" would be "all processed entries" but 
> there are cases where we "process an entry but not zap it".
>
> What you really only want to know is "was any entry not zapped", which 
> could be a simple input boolean variable passed into do_zap_pte_range?
>
> Because as soon as any entry was processed but  no zapped, you can 
> immediately give up on reclaiming that table.

Yes, we can set can_reclaim_pt to false when a !pte_none() entry is
found in count_pte_none().

> > Looking forward to your more review feedback on this series.
>
> Thanks for all your hard work on this, I'm only able to make slow 
> progress because I keep getting distracted by all different kinds of 
> things :(

It's OK, just take your time. :)

Thanks!

>