linux-kernel - Re: [PATCH 4/4] mm/damon/vaddr: indicate the target is invalid when 'nr

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Message-ID: <CAGjdHu=8pGmyBpVMpf-V=6w7hZHLmG4WH5EsNchn_+GqikTDxQ@mail.gmail.com>
Date:   Wed, 14 Sep 2022 12:02:05 +0800
From:   Kaixu Xia <xiakaixu1987@...il.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     akpm@...ux-foundation.org, damon@...ts.linux.dev,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Kaixu Xia <kaixuxia@...cent.com>
Subject: Re: [PATCH 4/4] mm/damon/vaddr: indicate the target is invalid when
 'nr_regions' is zero

On Tue, Sep 13, 2022 at 11:11 PM SeongJae Park <sj@...nel.org> wrote:
>
> On Tue, 13 Sep 2022 17:11:27 +0800 xiakaixu1987@...il.com wrote:
>
> > From: Kaixu Xia <kaixuxia@...cent.com>
> >
> > When 'init()' and 'update()' DAMON operations failed and the number
> > of the damon_target regions is zero,
>
> Well, I think that could be a temporal failure.  In the case, later call of
> 'update()' could success?
>
Yeah, the kdamond while() loop calls 'update()' periodically to fix this
temporary failure. But for extreme scenarios that 'update()' continues to fail,
we should have some ways to detect this case.

Thanks,
Kaixu
>
> Thanks,
> SJ
>
> > the kdamond would do nothing
> > to this monitoring target in this case. It makes no sense to run
> > kdamond when all of monitoring targets have no regions. So add the
> > judgement in 'target_valid()' operation to indicate the target is
> > invalid when 'nr_regions' is zero.
>
> >
> > Signed-off-by: Kaixu Xia <kaixuxia@...cent.com>
> > ---
> >  mm/damon/vaddr.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> > index 39ea48d9cc15..65ff98d49ec0 100644
> > --- a/mm/damon/vaddr.c
> > +++ b/mm/damon/vaddr.c
> > @@ -598,6 +598,9 @@ static bool damon_va_target_valid(void *target)
> >       struct damon_target *t = target;
> >       struct task_struct *task;
> >
> > +     if (!damon_nr_regions(t))
> > +             return false;
> > +
> >       task = damon_get_task_struct(t);
> >       if (task) {
> >               put_task_struct(task);
> > --
> > 2.27.0