linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: allocate blocks for pinned file

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Message-ID: <20190628021551.GA10489@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Thu, 27 Jun 2019 19:15:51 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: allocate blocks for pinned file

On 06/28, Chao Yu wrote:
> Hi Jaegeuk,
> 
> On 2019/6/28 1:05, Jaegeuk Kim wrote:
> > This patch allows fallocate to allocate physical blocks for pinned file.
> 
> Quoted from manual of fallocate(2):
> "
> Any subregion within the range specified by offset and len that did not contain
> data before the  call  will  be  initialized  to zero.
> 
> If  the  FALLOC_FL_KEEP_SIZE  flag  is specified in mode .... Preallocating
> zeroed blocks beyond the end of the file in this manner is useful for optimizing
> append workloads.
> "
> 
> As quoted description, our change may break the rule of fallocate(, mode = 0),
> because with after this change, we can't guarantee that preallocated physical
> block contains zeroed data
> 
> Should we introduce an additional ioctl for this case? Or maybe add one more
> flag in fallocate() for unzeroed block preallocation, not sure.

I thought like that, but this is a very corner case for the pinned file only in
f2fs. And, the pinned file is also indeed used by this purpose.

Thanks,

> 
> Thanks,
> 
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> >  fs/f2fs/file.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index e7c368db8185..cdfd4338682d 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1528,7 +1528,12 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
> >  	if (off_end)
> >  		map.m_len++;
> >  
> > -	err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_AIO);
> > +	if (f2fs_is_pinned_file(inode))
> > +		map.m_seg_type = CURSEG_COLD_DATA;
> > +
> > +	err = f2fs_map_blocks(inode, &map, 1, (f2fs_is_pinned_file(inode) ?
> > +						F2FS_GET_BLOCK_PRE_DIO :
> > +						F2FS_GET_BLOCK_PRE_AIO));
> >  	if (err) {
> >  		pgoff_t last_off;
> >  
> >