linux-ext4 - Re: [patch V2 5/7] fs/jbd2: Simplify journal_unmap

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Date:   Thu, 1 Aug 2019 11:04:26 +0200
From:   Jan Kara <jack@...e.cz>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>, linux-ext4@...r.kernel.org,
        Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.com>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Mark Fasheh <mark@...heh.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: [patch V2 5/7] fs/jbd2: Simplify journal_unmap_buffer()

On Thu 01-08-19 03:01:31, Thomas Gleixner wrote:
> journal_unmap_buffer() checks first whether the buffer head is a journal.
> If so it takes locks and then invokes jbd2_journal_grab_journal_head()
> followed by another check whether this is journal head buffer.
> 
> The double checking is pointless.
> 
> Replace the initial check with jbd2_journal_grab_journal_head() which
> alredy checks whether the buffer head is actually a journal.
> 
> Allows also early access to the journal head pointer for the upcoming
> conversion of state lock to a regular spinlock.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-ext4@...r.kernel.org
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Jan Kara <jack@...e.com>

Nice simplification. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> V2: New patch
> ---
>  fs/jbd2/transaction.c |    8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -2196,7 +2196,8 @@ static int journal_unmap_buffer(journal_
>  	 * holding the page lock. --sct
>  	 */
>  
> -	if (!buffer_jbd(bh))
> +	jh = jbd2_journal_grab_journal_head(bh);
> +	if (!jh)
>  		goto zap_buffer_unlocked;
>  
>  	/* OK, we have data buffer in journaled mode */
> @@ -2204,10 +2205,6 @@ static int journal_unmap_buffer(journal_
>  	jbd_lock_bh_state(bh);
>  	spin_lock(&journal->j_list_lock);
>  
> -	jh = jbd2_journal_grab_journal_head(bh);
> -	if (!jh)
> -		goto zap_buffer_no_jh;
> -
>  	/*
>  	 * We cannot remove the buffer from checkpoint lists until the
>  	 * transaction adding inode to orphan list (let's call it T)
> @@ -2329,7 +2326,6 @@ static int journal_unmap_buffer(journal_
>  	 */
>  	jh->b_modified = 0;
>  	jbd2_journal_put_journal_head(jh);
> -zap_buffer_no_jh:
>  	spin_unlock(&journal->j_list_lock);
>  	jbd_unlock_bh_state(bh);
>  	write_unlock(&journal->j_state_lock);
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR