From:   SeongJae Park <sj@kernel.org>
To:     Andrew Yang <andrew.yang@mediatek.com>
Cc:     SeongJae Park <sj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        wsd_upstream@mediatek.com, casper.lin@mediatek.com,
        damon@lists.linux.dev, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, stable@vger.kernel.org
Subject: Re: [PATCH] mm/damon/paddr: fix pin page problem
Date:   Tue, 21 Feb 2023 18:35:01 +0000
Message-Id: <20230221183501.132024-1-sj@kernel.org>
In-Reply-To: <20230221090313.15396-1-andrew.yang@mediatek.com>
References: 
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Hi Andrew,


On Tue, 21 Feb 2023 17:03:13 +0800 Andrew Yang <andrew.yang@mediatek.com> wrote:

> From: "andrew.yang" <andrew.yang@mediatek.com>
> 
> damon_get_page() would always increase page _refcount and
> isolate_lru_page() would increase page _refcount if the page's lru
> flag is set.
> 
> If a unevictable page isolated successfully, there will be two more
> _refcount. The one from isolate_lru_page() will be decreased in
> putback_lru_page(), but the other one from damon_get_page() will be
> left behind. This causes a pin page.
> 
> Whatever the case, the _refcount from damon_get_page() should be
> decreased.

Thank you for finding this issue!  I think the David suggested subject[1] is
better, though.

I think we could add below Fixes: and Cc: tags?

Fixes: 57223ac29584 ("mm/damon/paddr: support the pageout scheme")
Cc: <stable@vger.kernel.org> # 5.16.x

> 
> Signed-off-by: andrew.yang <andrew.yang@mediatek.com>
> ---
>  mm/damon/paddr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index e1a4315c4be6..56d8abd08fb1 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -223,8 +223,8 @@ static unsigned long damon_pa_pageout(struct damon_region *r)
>  			putback_lru_page(page);
>  		} else {
>  			list_add(&page->lru, &page_list);
> -			put_page(page);
>  		}
> +		put_page(page);

Seems your patch is not based on mm-unstable tree[2].  Could you please rebase
on it?

Also, let's remove the braces for the single statements[3].

[1] https://lore.kernel.org/damon/1b3e8e88-ed5c-7302-553f-4ddb3400d466@redhat.com/
[2] https://docs.kernel.org/next/mm/damon/maintainer-profile.html#scm-trees
[3] https://docs.kernel.org/process/coding-style.html?highlight=coding+style#placing-braces-and-spaces


Thanks,
SJ

>  	}
>  	applied = reclaim_pages(&page_list);
>  	cond_resched();
> -- 
> 2.18.0