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

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Message-ID: <YJN0nTgadoq8vDaG@google.com>
Date:   Wed, 5 May 2021 21:46:21 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     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: [PATCH] f2fs: set file as cold when file defragmentation

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
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?

> 
> 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;
> >