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

[Aneesh Kumar K V]

On 4/27/22 10:08 AM, Yu Zhao wrote:
> 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.

should we then use a mmu notifier variant of clear_young in 
lru_gen_look_around() ?

-aneesh