linux-kernel - Re: [PATCHv1 2/2] jbd2: Remove CONFIG_JBD2_DEBUG to update t_max

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Date:   Mon, 24 Jan 2022 10:12:43 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jan Kara <jack@...e.com>,
        tytso@....edu
Subject: Re: [PATCHv1 2/2] jbd2: Remove CONFIG_JBD2_DEBUG to update t_max_wait

On Sun 23-01-22 22:53:28, Ritesh Harjani wrote:
> CONFIG_JBD2_DEBUG and jbd2_journal_enable_debug knobs were added in
> update_t_max_wait(), since earlier it used to take a spinlock for updating
> t_max_wait, which could cause a bottleneck while starting a txn
> (start_this_handle()).
> Since in previous patch, we have killed t_handle_lock completely, we
> could get rid of this debug config and knob to let t_max_wait be updated
> by default again.
> 
> Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>

Sounds fine. Feel free to add:

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

								Honza

> ---
>  fs/jbd2/transaction.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 68dd7de49aff..77634e2e118e 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -141,20 +141,19 @@ static void jbd2_get_transaction(journal_t *journal,
>   * t_max_wait is carefully updated here with use of atomic compare exchange.
>   * Note that there could be multiplre threads trying to do this simultaneously
>   * hence using cmpxchg to avoid any use of locks in this case.
> + * With this t_max_wait can be updated w/o enabling jbd2_journal_enable_debug.
>   */
>  static inline void update_t_max_wait(transaction_t *transaction,
>  				     unsigned long ts)
>  {
> -#ifdef CONFIG_JBD2_DEBUG
>  	unsigned long oldts, newts;
> -	if (jbd2_journal_enable_debug &&
> -	    time_after(transaction->t_start, ts)) {
> +
> +	if (time_after(transaction->t_start, ts)) {
>  		newts = jbd2_time_diff(ts, transaction->t_start);
>  		oldts = READ_ONCE(transaction->t_max_wait);
>  		while (oldts < newts)
>  			oldts = cmpxchg(&transaction->t_max_wait, oldts, newts);
>  	}
> -#endif
>  }
> 
>  /*
> --
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR