Re: [PATCH 8/8] mm: Remove PG_reclaim

[Yu Zhao <yuzhao@google.com>]

On Tue, Jan 14, 2025 at 1:30 AM Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> On Mon, Jan 13, 2025 at 03:28:43PM +0000, Matthew Wilcox wrote:
> > On Mon, Jan 13, 2025 at 11:34:53AM +0200, Kirill A. Shutemov wrote:
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index caadbe393aa2..beba72da5e33 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -686,6 +686,8 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
> > >             folio_set_young(newfolio);
> > >     if (folio_test_idle(folio))
> > >             folio_set_idle(newfolio);
> > > +   if (folio_test_readahead(folio))
> > > +           folio_set_readahead(newfolio);
> > >
> > >     folio_migrate_refs(newfolio, folio);
> > >     /*
> >
> > Not a problem with this patch ... but aren't we missing a
> > test_dropbehind / set_dropbehind pair in this function?  Or are we
> > prohibited from migrating a folio with the dropbehind flag set
> > somewhere?
>
> Hm. Good catch.
>
> We might want to drop clean dropbehind pages instead migrating them.
>
> But I am not sure about dirty ones. With slow backing storage it might be
> better for the system to migrate them instead of keeping them in the old
> place for potentially long time.
>
> Any opinions?
>
> > > +++ b/mm/swap.c
> > > @@ -221,22 +221,6 @@ static void lru_move_tail(struct lruvec *lruvec, struct folio *folio)
> > >     __count_vm_events(PGROTATED, folio_nr_pages(folio));
> > >  }
> > >
> > > -/*
> > > - * Writeback is about to end against a folio which has been marked for
> > > - * immediate reclaim.  If it still appears to be reclaimable, move it
> > > - * to the tail of the inactive list.
> > > - *
> > > - * folio_rotate_reclaimable() must disable IRQs, to prevent nasty races.
> > > - */
> > > -void folio_rotate_reclaimable(struct folio *folio)
> > > -{
> > > -   if (folio_test_locked(folio) || folio_test_dirty(folio) ||
> > > -       folio_test_unevictable(folio))
> > > -           return;
> > > -
> > > -   folio_batch_add_and_move(folio, lru_move_tail, true);
> > > -}
> >
> > I think this is the last caller of lru_move_tail(), which means we can
> > get rid of fbatches->lru_move_tail and the local_lock that protects it.
> > Or did I miss something?
>
> I see lru_move_tail() being used by lru_add_drain_cpu().

That can be deleted too, since you've already removed the producer to
fbatches->lru_move_tail.