Re: [PATCH v10 07/14] mm: multi-gen LRU: exploit locality in rmap

[Yu Zhao]

On Tue, Apr 26, 2022 at 10:33 PM Aneesh Kumar K.V
<aneesh.kumar@xxxxxxxxxxxxx> wrote:
>
> Yu Zhao <yuzhao@xxxxxxxxxx> writes:
>
> ....
>
>  diff --git a/mm/rmap.c b/mm/rmap.c
> > index fedb82371efe..7cb7ef29088a 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -73,6 +73,7 @@
> >  #include <linux/page_idle.h>
> >  #include <linux/memremap.h>
> >  #include <linux/userfaultfd_k.h>
> > +#include <linux/mm_inline.h>
> >
> >  #include <asm/tlbflush.h>
> >
> > @@ -821,6 +822,12 @@ static bool folio_referenced_one(struct folio *folio,
> >               }
> >
> >               if (pvmw.pte) {
> > +                     if (lru_gen_enabled() && pte_young(*pvmw.pte) &&
> > +                         !(vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))) {
> > +                             lru_gen_look_around(&pvmw);
> > +                             referenced++;
> > +                     }
>
> Is it required to update referenced here? we do that below after
> clearing the young bit. Or is the goal to identify whether we found any
> young pte around?

referenced++ is needed because lru_gen_look_around() also clears the
young bit in pvmw.pte. And ptep_clear_flush_young_notify() will return
false unless mmu notifier returns true.

> > +
> >                       if (ptep_clear_flush_young_notify(vma, address,
> >                                               pvmw.pte)) {
> >                               /*