On 22/01/13 12:27PM, Jan Kara wrote:
> 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
I too had this thought in mind. Thanks for taking a deeper look into it :)
>
> 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.
Thanks for providing the details Jan :)
Agree with jbd2_journal_extend(). I did looked a bit around t_max_wait and
I agree that something like above could work. I will spend some more time around
that code and will submit those changes together in v2.
-ritesh
>
> 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
