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From:   SeongJae Park <sj@kernel.org>
To:     xiakaixu1987@gmail.com
Cc:     sj@kernel.org, akpm@linux-foundation.org, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Kaixu Xia <kaixuxia@tencent.com>
Subject: Re: [PATCH 4/4] mm/damon/vaddr: indicate the target is invalid when 'nr_regions' is zero
Date:   Tue, 13 Sep 2022 15:11:14 +0000
Message-Id: <20220913151114.103184-1-sj@kernel.org>
In-Reply-To: <1663060287-30201-5-git-send-email-kaixuxia@tencent.com>
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On Tue, 13 Sep 2022 17:11:27 +0800 xiakaixu1987@gmail.com wrote:

> From: Kaixu Xia <kaixuxia@tencent.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?


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@tencent.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