Date:   Wed, 12 May 2021 17:45:18 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>
CC:     Daejun Park <daejun7.park@...sung.com>,
        "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 05/11, Chao Yu wrote:
>> On 2021/5/11 14:41, Daejun Park wrote:
>> > > 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.
>> 
>> Alright,
>> 
>> > I think the user will call the defrag ioctl for the files that have been updated.
>> 
>> Sadly, I don't see there is any user of this defragment interface since it was
>> been introduced... so I really don't know the real use scenario of this interface
>> now.
>> 
>> > 
>> > 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?
>> 
>> bool f2fs_should_update_inplace(struct inode *inode, struct f2fs_io_info *fio)
>> {
>>         if (f2fs_is_pinned_file(inode))
>>                 return true;
>> 
>>         /* if this is cold file, we should overwrite to avoid fragmentation */
>>         if (file_is_cold(inode))
>>                 return true;
>> 
>> If cold bit was set, later rewrite in defragment interface can only trigger
>> IPU due to above IPU policy check, so after this interface, file is still
>> fragmented... what's the difference compared to just setting cold bit via
>> setxattr?
>> 
>> And if user know that he will trigger less update and more read in the file,
>> why not just calling setxattr("system.advise", cold_bit) to set the file as
>> cold before it becomes fragmented, e.g. at the time of file creation?
> 
>yea, actually user can set it whatever they want after defragment. :P

I agree Chao yu's opinion so I drop this patch.

Thanks,
Daejun

> 
>> 
>> Thanks,
>> 
>> > 
>> > 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;
>> > > > > > > > > > 
>> > > > > > > > .
>> > > > > > > > 
>> > > > > > .
>> > > > > > 
>> > > > .
>> > > > 
>> > > 
>> > > 
>> > .
>> > 
> 
> 
>  

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