linux-kernel - Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa

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Date:   Tue,  7 Mar 2023 18:00:23 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     SeongJae Park <sj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, damon@...ts.linux.dev
Subject: Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa_young()

On Tue, 7 Mar 2023 09:22:33 +0800 Kefeng Wang <wangkefeng.wang@...wei.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@...wei.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@...wei.com> wrote:
> >>>>
> >>>>> Omit three lines by unified folio_put(), and make code more clear.
> >>>>>
> >>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.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