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

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Date:   Wed, 4 Nov 2020 13:25:30 -0800
From:   harshad shirwadkar <harshadshirwadkar@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>
Subject: Re: [PATCH 05/10] jbd2: fix fast commit journalling APIs

On Tue, Nov 3, 2020 at 8:38 AM Jan Kara <jack@...e.cz> wrote:
>
> 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.
Okay thanks for pointing this out. I'll break this commit into logical
patches for the next version.
>
> > 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."
Ack
>
> > +      * 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.
Ack,

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