On Thu 13-01-22 08:56:29, Ritesh Harjani wrote:
> Since jbd2_journal_wait_updates() uses waitq based on t_updates atomic_t
> variable. So from code review it looks like we don't need to use
> t_handle_lock spinlock for checking t_updates value.
> Hence this patch gets rid of the spinlock protection in
> jbd2_journal_wait_updates()
>
> Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
This patch looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Actually looking at it, t_handle_lock seems to be very much unused. I agree
we don't need it when waiting for outstanding handles but the only
remaining uses are:
1) jbd2_journal_extend() where it is not needed either - we use
atomic_add_return() to manipulate t_outstanding_credits and hold
j_state_lock for reading which provides us enough exclusion.
2) update_t_max_wait() - this is the only valid use of t_handle_lock but we
can just switch it to cmpxchg loop with a bit of care. Something like:
unsigned long old;
ts = jbd2_time_diff(ts, transaction->t_start);
old = transaction->t_max_wait;
while (old < ts)
old = cmpxchg(&transaction->t_max_wait, old, ts);
So perhaps you can add two more patches to remove other t_handle_lock uses
and drop it completely.
Honza
> ---
> include/linux/jbd2.h | 4 ----
> 1 file changed, 4 deletions(-)
>
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 34b051aa9009..9bef47622b9d 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1768,22 +1768,18 @@ static inline void jbd2_journal_wait_updates(journal_t *journal)
> if (!commit_transaction)
> return;
>
> - spin_lock(&commit_transaction->t_handle_lock);
> while (atomic_read(&commit_transaction->t_updates)) {
> DEFINE_WAIT(wait);
>
> prepare_to_wait(&journal->j_wait_updates, &wait,
> TASK_UNINTERRUPTIBLE);
> if (atomic_read(&commit_transaction->t_updates)) {
> - spin_unlock(&commit_transaction->t_handle_lock);
> write_unlock(&journal->j_state_lock);
> schedule();
> write_lock(&journal->j_state_lock);
> - spin_lock(&commit_transaction->t_handle_lock);
> }
> finish_wait(&journal->j_wait_updates, &wait);
> }
> - spin_unlock(&commit_transaction->t_handle_lock);
> }
>
> /*
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
