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Subject: Re: [f2fs-dev] [PATCH] f2fs: change write_hint for hot/warm nodes
To:     <daejun7.park@samsung.com>,
        "jaegeuk@kernel.org" <jaegeuk@kernel.org>,
        "chao@kernel.org" <chao@kernel.org>
CC:     yongmyung lee <ymhungry.lee@samsung.com>,
        Jieon Seol <jieon.seol@samsung.com>,
        Sang-yoon Oh <sangyoon.oh@samsung.com>,
        Mankyu PARK <manq.park@samsung.com>,
        Sung-Jun Park <sungjun07.park@samsung.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-f2fs-devel@lists.sourceforge.net" 
        <linux-f2fs-devel@lists.sourceforge.net>,
        Keoseong Park <keosung.park@samsung.com>,
        SEUNGUK SHIN <seunguk.shin@samsung.com>,
        "Jinyoung CHOI" <j-young.choi@samsung.com>,
        Jaemyung Lee <jaemyung.lee@samsung.com>
References: <CGME20201103064039epcms2p30ecac0e7cefff0d50745f2e2e61ce38e@epcms2p3>
 <20201103064039epcms2p30ecac0e7cefff0d50745f2e2e61ce38e@epcms2p3>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <609445f8-de3b-eb79-449c-020125799449@huawei.com>
Date:   Tue, 3 Nov 2020 16:28:49 +0800
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On 2020/11/3 14:40, Daejun Park wrote:
>>From 818a76a9aee5bf225565264274d211edb07bae7d Mon Sep 17 00:00:00 2001
> From: Daejun Park <daejun7.park@samsung.com>
> Date: Tue, 3 Nov 2020 15:30:26 +0900
> 
> 
> In the fs-based mode of F2FS, the mapping of hot/warm node to
> WRITE_LIFE_NOT_SET should be changed to WRITE_LIFE_SHORT.
> 
> As a result of analyzing the write pattern of f2fs using real workload,
> hot/warm nodes have high update ratio close to hot data.[*]
> However, F2FS passes write hints for hot/warm nodes as WRITE_LIFE_NOT_SET.
> 
> Furthermore, WRITE_LIFE_NOT_SET is a default value of write hint when it is
> not provided from the file system.
> In storage, write_hint is used to distinguish streams (e.g. NVMe).
> So, the hot/warm node of F2FS is not distinguished from other write_hints,
> which can make the wrong stream seperation.
> 
> * Liang, Yu, et al. "An empirical study of F2FS on mobile devices." 2017
> IEEE 23rd International Conference on Embedded and Real-Time Computing
> Systems and Applications (RTCSA).

Could you please update Documentation/filesystems/f2fs.rst as well?

Thanks,

> 
> Signed-off-by: Daejun Park <daejun7.park@samsung.com>
> ---
>   fs/f2fs/segment.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 1596502f7375..7b42bb10c6c3 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -3208,7 +3208,7 @@ enum rw_hint f2fs_io_type_to_rw_hint(struct f2fs_sb_info *sbi,
>   				return WRITE_LIFE_EXTREME;
>   		} else if (type == NODE) {
>   			if (temp == WARM || temp == HOT)
> -				return WRITE_LIFE_NOT_SET;
> +				return WRITE_LIFE_SHORT;
>   			else if (temp == COLD)
>   				return WRITE_LIFE_NONE;
>   		} else if (type == META) {
>