linux-kernel - RE: Re: [PATCH] f2fs: set file as cold when file defragmentation

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Date:   Tue, 11 May 2021 15:41:56 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Daejun Park <daejun7.park@...sung.com>
CC:     "chao@...nel.org" <chao@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: RE: Re: [PATCH] f2fs: set file as cold when file defragmentation

>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?

It is just my idea for defragmentation, not Samsung.
I think the user will call the defrag ioctl for the files that have been updated.

On the other hand, I think FS should be able to support defrag file even 
when in-place update is applied. What do you think?

Thanks,
Daejun
> 
>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@...sung.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;
>>>>>>>>
>>>>>> .
>>>>>>
>>>> .
>>>>
>> .
>> 
> 
> 
>