linux-kernel - Re: [PATCH v2 09/11] btrfs: convert to multigrain timestamps

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Date: Mon, 01 Jul 2024 09:57:43 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Josef Bacik <josef@...icpanda.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner
 <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Steven Rostedt
 <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Chandan Babu R
 <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>, Theodore
 Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, Chris
 Mason <clm@...com>, David Sterba <dsterba@...e.com>, Hugh Dickins
 <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen
 <ak@...ux.intel.com>,  kernel-team@...com, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org,  linux-trace-kernel@...r.kernel.org,
 linux-xfs@...r.kernel.org,  linux-ext4@...r.kernel.org,
 linux-btrfs@...r.kernel.org, linux-mm@...ck.org,  linux-nfs@...r.kernel.org
Subject: Re: [PATCH v2 09/11] btrfs: convert to multigrain timestamps

On Mon, 2024-07-01 at 09:49 -0400, Josef Bacik wrote:
> On Mon, Jul 01, 2024 at 06:26:45AM -0400, Jeff Layton wrote:
> > Enable multigrain timestamps, which should ensure that there is an
> > apparent change to the timestamp whenever it has been written after
> > being actively observed via getattr.
> > 
> > Beyond enabling the FS_MGTIME flag, this patch eliminates
> > update_time_for_write, which goes to great pains to avoid in-memory
> > stores. Just have it overwrite the timestamps unconditionally.
> > 
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > ---
> >  fs/btrfs/file.c  | 25 ++++---------------------
> >  fs/btrfs/super.c |  3 ++-
> >  2 files changed, 6 insertions(+), 22 deletions(-)
> > 
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index d90138683a0a..409628c0c3cc 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -1120,26 +1120,6 @@ void btrfs_check_nocow_unlock(struct
> > btrfs_inode *inode)
> >  	btrfs_drew_write_unlock(&inode->root->snapshot_lock);
> >  }
> >  
> > -static void update_time_for_write(struct inode *inode)
> > -{
> > -	struct timespec64 now, ts;
> > -
> > -	if (IS_NOCMTIME(inode))
> > -		return;
> > -
> > -	now = current_time(inode);
> > -	ts = inode_get_mtime(inode);
> > -	if (!timespec64_equal(&ts, &now))
> > -		inode_set_mtime_to_ts(inode, now);
> > -
> > -	ts = inode_get_ctime(inode);
> > -	if (!timespec64_equal(&ts, &now))
> > -		inode_set_ctime_to_ts(inode, now);
> > -
> > -	if (IS_I_VERSION(inode))
> > -		inode_inc_iversion(inode);
> > -}
> > -
> >  static int btrfs_write_check(struct kiocb *iocb, struct iov_iter
> > *from,
> >  			     size_t count)
> >  {
> > @@ -1171,7 +1151,10 @@ static int btrfs_write_check(struct kiocb
> > *iocb, struct iov_iter *from,
> >  	 * need to start yet another transaction to update the
> > inode as we will
> >  	 * update the inode when we finish writing whatever data
> > we write.
> >  	 */
> > -	update_time_for_write(inode);
> > +	if (!IS_NOCMTIME(inode)) {
> > +		inode_set_mtime_to_ts(inode,
> > inode_set_ctime_current(inode));
> > +		inode_inc_iversion(inode);
> 
> You've dropped the
> 
> if (IS_I_VERSION(inode))
> 
> check here, and it doesn't appear to be in inode_inc_iversion.  Is
> there a
> reason for this?  Thanks,
> 

AFAICT, btrfs always sets SB_I_VERSION. Are there any cases where it
isn't? If so, then I can put this check back. I'll make a note about it
in the changelog if not.

-- 
Jeff Layton <jlayton@...nel.org>