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

SeongJae Park
2023-03-07T18:00:32Z

On Tue, 7 Mar 2023 09:22:33 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:

>
>
> On 2023/3/7 5:27, SeongJae Park wrote:
> > Hi Kefeng,
> >
> > On Mon, 6 Mar 2023 09:56:49 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> 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@huawei.com> wrote:
> >>>>
> >>>>> Omit three lines by unified folio_put(), and make code more clear.
> >>>>>
> >>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> >>>>> ---
> >>>>> 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.

Ah, you're right. Thank you for kind explanation. I was out of my mind for
some reason. Maybe we could just do 'goto out' in the branch.

Thanks,
SJ