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Subject: Re: [PATCH] f2fs: set file as cold when file defragmentation
To:     Jaegeuk Kim <jaegeuk@kernel.org>, <daejun7.park@samsung.com>
CC:     "chao@kernel.org" <chao@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-f2fs-devel@lists.sourceforge.net" 
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From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <fc7f1b2b-60ea-eb12-3195-7b3ad0b3adc2@huawei.com>
Date:   Tue, 11 May 2021 14:07:29 +0800
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On 2021/5/11 13:09, Jaegeuk Kim wrote:
> On 05/11, Chao Yu wrote:
>> On 2021/5/10 22:47, Jaegeuk Kim wrote:
>>> On 05/06, Chao Yu wrote:
>>>> On 2021/5/6 12:46, Jaegeuk Kim wrote:
>>>>> On 05/06, Chao Yu wrote:
>>>>>> On 2021/4/29 14:20, Daejun Park wrote:
>>>>>>> In file defragmentation by ioctl, all data blocks in the file are
>>>>>>> re-written out-of-place. File defragmentation implies user will not update
>>>>>>> and mostly read the file. So before the defragmentation, we set file
>>>>>>> temperature as cold for better block allocation.
>>>>>>
>>>>>> I don't think all fragmented files are cold, e.g. db file.
>>>>>
>>>>> I have a bit different opinion. I think one example would be users want to
>>>>> defragment a file, when the they want to get higher read bandwidth for
>>>>
>>>> Multimedia file was already defined as cold file now via default extension
>>>> list?
>>>
>>> I just gave an example. And default is default.
>>>
>>>>
>>>>> usually multimedia files. That's likely to be cold files. Moreover, I don't
>>>>> think they want to defragment db files which will be fragmented soon?
>>>>
>>>> I guess like db files have less update but more access?
>>>
>>> I think both, and we set it as hot.
>>
>> Then hot and cold bit will set to the same db file after defragmentation?
> 
> Do you set cold bit to db files? I mean, generally db is not cold, but hot.

I never set cold bit to db files, I mean if we defragment db file which
has less update and more access, db file may have bot hot and cold bit.

To Daejun, may I ask that is Samsung planning to use this defragment ioctl
in products? what's the user scenario?

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> We have separated interface (via f2fs_xattr_advise_handler, e.g. setfattr -n
>>>>>> "system.advise" -v value) to indicate this file is a hot/cold file, so my
>>>>>> suggestion is after file defragmentation, if you think this file is cold, and
>>>>>> use setxattr() to set it as cold.
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: Daejun Park <daejun7.park@samsung.com>
>>>>>>> ---
>>>>>>>      fs/f2fs/file.c | 3 +++
>>>>>>>      1 file changed, 3 insertions(+)
>>>>>>>
>>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>>>>> index d697c8900fa7..dcac965a05fe 100644
>>>>>>> --- a/fs/f2fs/file.c
>>>>>>> +++ b/fs/f2fs/file.c
>>>>>>> @@ -2669,6 +2669,9 @@ static int f2fs_defragment_range(struct f2fs_sb_info *sbi,
>>>>>>>      	map.m_len = pg_end - pg_start;
>>>>>>>      	total = 0;
>>>>>>> +	if (!file_is_cold(inode))
>>>>>>> +		file_set_cold(inode);
>>>>>>> +
>>>>>>>      	while (map.m_lblk < pg_end) {
>>>>>>>      		pgoff_t idx;
>>>>>>>      		int cnt = 0;
>>>>>>>
>>>>> .
>>>>>
>>> .
>>>
> .
>