linux-ext4 - Re: [PATCH 05/10] jbd2: fix fast commit journalling APIs

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Date:   Tue, 3 Nov 2020 17:38:50 +0100
From:   Jan Kara <jack@...e.cz>
To:     Harshad Shirwadkar <harshadshirwadkar@...il.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz
Subject: Re: [PATCH 05/10] jbd2: fix fast commit journalling APIs

On Sat 31-10-20 13:05:13, Harshad Shirwadkar wrote:
> This patch adds a few misc fixes for jbd2 fast commit functions.
> 
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>

Please no "misc fixes" patches. If you have trouble writing good
explanatory changelog, it's usually a sign you're trying to cram too much
into a single commit :). In this case I'd split it into 3 changes:

1) TODO update.
2) Removal of j_state_lock protection (with comment updates)
3) Fix of journal->j_running_transaction->t_tid handling.

> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 9b4e87a0068b..df1285da7276 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -946,7 +946,9 @@ struct journal_s
>  	 * @j_fc_off:
>  	 *
>  	 * Number of fast commit blocks currently allocated.
> -	 * [j_state_lock].
> +	 * [j_state_lock]. During the commit path, this variable is not

Please remove the [j_state_lock] annotation when the entry isn't really
protected by j_state_lock... Also I'd maybe rephrase the comment like
"Accessed only during fastcommit, currenly only a single process can
perform fastcommit at a time."

> +	 * protected by j_state_lock since only one process performs commit
> +	 * at a time.
>  	 */
>  	unsigned long		j_fc_off;
>  
> @@ -1110,7 +1112,9 @@ struct journal_s
>  
>  	/**
>  	 * @j_fc_wbuf: Array of fast commit bhs for
> -	 * jbd2_journal_commit_transaction.
> +	 * jbd2_journal_commit_transaction. During the commit path, this
> +	 * variable is not protected by j_state_lock since only one process
> +	 * performs commit at a time.
>  	 */
>  	struct buffer_head	**j_fc_wbuf;

Here the bh's aren't really used in jbd2_journal_commit_transaction() are
they? Please fix that when updating the comment. Also I'd find a
reformulation like I suggested for the comment above more comprehensible.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR