RE: Re: [f2fs-dev] [PATCH] f2fs: change write_hint for hot/warm nodes

[Daejun Park <daejun7.park@samsung.com>]

>>>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) {
>> 
>
>