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Subject: RE: Re: [f2fs-dev] [PATCH] f2fs: change write_hint for hot/warm
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Sender: Daejun Park <daejun7.park@samsung.com>
From:   Daejun Park <daejun7.park@samsung.com>
To:     Chao Yu <yuchao0@huawei.com>,
        Daejun Park <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>
In-Reply-To: <609445f8-de3b-eb79-449c-020125799449@huawei.com>
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Date:   Tue, 03 Nov 2020 17:33:06 +0900
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>>>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,

Sure, I will make it next patch.

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) {
>> 
>
>