From:   SeongJae Park <sj@kernel.org>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     SeongJae Park <sj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, damon@lists.linux.dev
Subject: Re: [PATCH -next] mm/damon/paddr: minor refactor of damon_pa_pageout()
Date:   Thu,  2 Mar 2023 16:47:06 +0000
Message-Id: <20230302164706.85999-1-sj@kernel.org>
In-Reply-To: <20230302144926.40012-1-wangkefeng.wang@huawei.com>
References: 
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Precedence: bulk

Hi Kefeng,

On Thu, 2 Mar 2023 22:49:26 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:

> Omit two lines by converting if(!folio_isolate_lru()) to
> if(folio_isolate_lru()).
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  mm/damon/paddr.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index 6c655d9b5639..a557f3c9300f 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -246,14 +246,12 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
>  
>  		folio_clear_referenced(folio);
>  		folio_test_clear_young(folio);
> -		if (!folio_isolate_lru(folio)) {
> -			folio_put(folio);
> -			continue;
> +		if (folio_isolate_lru(folio)) {
> +			if (folio_test_unevictable(folio))
> +				folio_putback_lru(folio);
> +			else
> +				list_add(&folio->lru, &folio_list);
>  		}
> -		if (folio_test_unevictable(folio))
> -			folio_putback_lru(folio);
> -		else
> -			list_add(&folio->lru, &folio_list);
>  		folio_put(folio);
>  	}

This looks ok to me, thank you for your effort!  Nevertheless, I don't like
increasing depth as much as number of lines.  The
more-than-3-levels-of-indentation[1] warning is not always right, but this 4
levels of indentation is not making me so exciting.

What do you think about adding put_continue label and using it, not only here,
but also above part?  For example:

    --- a/mm/damon/paddr.c
    +++ b/mm/damon/paddr.c
    @@ -239,21 +239,18 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
                    if (!folio)
                            continue;
    
    -               if (damos_pa_filter_out(s, folio)) {
    -                       folio_put(folio);
    -                       continue;
    -               }
    +               if (damos_pa_filter_out(s, folio))
    +                       goto put_continue;
    
                    folio_clear_referenced(folio);
                    folio_test_clear_young(folio);
    -               if (!folio_isolate_lru(folio)) {
    -                       folio_put(folio);
    -                       continue;
    -               }
    +               if (!folio_isolate_lru(folio))
    +                       goto put_continue;
                    if (folio_test_unevictable(folio))
                            folio_putback_lru(folio);
                    else
                            list_add(&folio->lru, &folio_list);
    +put_continue:
                    folio_put(folio);
            }
            applied = reclaim_pages(&folio_list);

It omits three lines.

    $ git diff --stat
     mm/damon/paddr.c | 13 +++++--------
     1 file changed, 5 insertions(+), 8 deletions(-)

[1] https://docs.kernel.org/process/coding-style.html#indentation


Thanks,
SJ

>  	applied = reclaim_pages(&folio_list);
> -- 
> 2.35.3
> 
>