Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa_young()

[Kefeng Wang]

On 2023/3/7 5:27, SeongJae Park wrote:
> Hi Kefeng,
>
> On Mon, 6 Mar 2023 09:56:49 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
> > On 2023/3/6 9:10, Kefeng Wang wrote:
> > > On 2023/3/4 2:39, SeongJae Park wrote:
> > > > Hi Kefeng,
> > > >
> > > > On Fri, 3 Mar 2023 16:43:42 +0800 Kefeng Wang
> > > > <wangkefeng.wang@xxxxxxxxxx> wrote:
> > > >
> > > > > Omit three lines by unified folio_put(), and make code more clear.
> > > > >
> > > > > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > > > > ---
> > > > >    mm/damon/paddr.c | 11 ++++-------
> > > > >    1 file changed, 4 insertions(+), 7 deletions(-)
> > > > >
> > > > > diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> > > > > index 3fda00a0f786..2ef9db0189ca 100644
> > > > > --- a/mm/damon/paddr.c
> > > > > +++ b/mm/damon/paddr.c
> > > > > @@ -130,24 +130,21 @@ static bool damon_pa_young(unsigned long paddr,
> > > > > unsigned long *folio_sz)
> > > > >                accessed = false;
> > > > >            else
> > > > >                accessed = true;
> > > > > -        folio_put(folio);
> > > > >            goto out;
> > > >
> > > > Because you moved 'out' label to not include *folio_sz setting,
> > > > folio_sz will
> > > > not set in this case.  It should be set.
> > > oh, it should be fixed.
> > > > >        }
> > > > >        need_lock = !folio_test_anon(folio) || folio_test_ksm(folio);
> > > > > -    if (need_lock && !folio_trylock(folio)) {
> > > > > -        folio_put(folio);
> > > > > -        return false;
> > > > > -    }
> >
> > Hi SJ,  apart from above issue, it looks that this branch need the
> > folio_size() setting, right?
>
> folio_sz is effectively used by caller of damon_pa_young() only if this
> function returns true, so this branch doesn't need to set folio_sz.

__damon_pa_check_access() store last_addr, last_accessed and 
last_folio_sz, even damon_pa_young() return false, the following check 
still use last_folio_sz,

  ALIGN_DOWN(last_addr, last_folio_sz) == ALIGN_DOWN(r->sampling_addr, 
last_folio_sz)

but last_folio_sz is not up to date, so I think it need to update, and 
update last_folio_sz is harmless, which could let's unify the return 
path, correct me if I am wrong.