Re: [PATCH v1] mm/rmap: cleanup partially-mapped handling in __folio_remove_rmap()

[David Hildenbrand]

On 24.06.24 13:48, Yosry Ahmed wrote:
> On Tue, Jun 18, 2024 at 8:10 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
> > Let's simplify and reduce code indentation. In the RMAP_LEVEL_PTE case, we
> > already check for nr when computing partially_mapped.
> >
> > For RMAP_LEVEL_PMD, it's a bit more confusing. Likely, we don't need the
> > "nr" check, but we could have "nr < nr_pmdmapped" also if we stumbled
> > into the "/* Raced ahead of another remove and an add? */" case. So
> > let's simply move the nr check in there.
> >
> > Note that partially_mapped is always false for small folios.
> >
> > No functional change intended.
> >
> > Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
> Makes sense to me. FWIW:
>
> Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
>
> > ---
> >   mm/rmap.c | 10 ++++------
> >   1 file changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index afec4b6800caf..aa900e46cdf82 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1551,11 +1551,12 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
> >                          }
> >                  }
> >
> > -               partially_mapped = nr < nr_pmdmapped;
> > +               partially_mapped = nr && nr < nr_pmdmapped;
> >                  break;
> >          }
> >
> > -       if (nr) {
> > +       if (partially_mapped && folio_test_anon(folio) &&
> > +           list_empty(&folio->_deferred_list))
> >                  /*
> >                   * Queue anon large folio for deferred split if at least one
> >                   * page of the folio is unmapped and at least one page
> > @@ -1563,10 +1564,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
> >                   *
> >                   * Check partially_mapped first to ensure it is a large folio.
> >                   */
> > -               if (folio_test_anon(folio) && partially_mapped &&
> > -                   list_empty(&folio->_deferred_list))
> > -                       deferred_split_folio(folio);
> > -       }
> > +               deferred_split_folio(folio);
>
> FWIW, I prefer moving the comment out of the one-line if block as you
> originally suggested in [1].
>
> [1]https://lore.kernel.org/lkml/1a408ed1-7e81-457e-a205-db274b4d6b78@xxxxxxxxxx/

Sorry for the late reply, crazy times here.

Let me do that and resend, thanks!

--
Cheers,

David / dhildenb