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

SeongJae Park
2023-03-06T21:27:33Z

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.

Thanks,
SJ

>
> Thanks
>
> >>> + if (need_lock && !folio_trylock(folio))
> >>> + goto out;
> >>> rmap_walk(folio, &rwc);
> >>> if (need_lock)
> >>> folio_unlock(folio);
> >>> - folio_put(folio);
> >>> -out:
> >>> *folio_sz = folio_size(folio);
> >>> +out:
> >>> + folio_put(folio);
> >>
> >> Before this change, folio_size() is called after folio_put().
> >> Shouldn't it be
> >> called before folio_put()? If so, could we make a separate fix for
> >> that first,
> >> and then make this change on top of it, so that it can be easily
> >> applied to
> >> relevant stable kernels?
> >>
> > Yes， I could separate it, after folio_put(), the folio could be
> > re-allocated and the folio_size calculation is not right.
> >>
> >> Thanks,
> >> SJ
> >>
> >>> return accessed;
> >>> }
> >>> --
> >>> 2.35.3
> >>>
> >>>
>