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

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Date: Mon, 1 Jul 2024 09:49:36 -0400
From: Josef Bacik <josef@...icpanda.com>
To: Jeff Layton <jlayton@...nel.org>
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, 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,

Josef