From: Jan Kara <jack@suse.cz>
To: Ritesh Harjani <riteshh@linux.ibm.com>
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, Jan Kara <jack@suse.com>,
Andreas Dilger <adilger.kernel@dilger.ca>,
tytso@mit.edu, Eric Whitney <enwlinux@gmail.com>
Subject: Re: [PATCH 6/6] jbd2: No need to use t_handle_lock in jbd2_journal_wait_updates
Date: Thu, 13 Jan 2022 12:27:49 +0100 [thread overview]
Message-ID: <20220113112749.d5tfszcksvxvshnn@quack3.lan> (raw)
In-Reply-To: <e7e0f8c54306591a3a9c8fead1e0e54358052ab6.1642044249.git.riteshh@linux.ibm.com>
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@linux.ibm.com>
This patch looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
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@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2022-01-13 11:27 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-13 3:26 [PATCH 0/6] ext4/jbd2: inline_data fixes and some cleanups Ritesh Harjani
2022-01-13 3:26 ` [PATCH 1/6] ext4: Fix error handling in ext4_restore_inline_data() Ritesh Harjani
2022-01-13 10:58 ` Jan Kara
2022-01-13 3:26 ` [PATCH 2/6] ext4: Remove redundant max inline_size check in ext4_da_write_inline_data_begin() Ritesh Harjani
2022-01-13 10:58 ` Jan Kara
2022-01-13 3:26 ` [PATCH 3/6] ext4: Fix error handling in ext4_fc_record_modified_inode() Ritesh Harjani
2022-01-13 11:00 ` Jan Kara
2022-01-13 3:26 ` [PATCH 4/6] jbd2: Cleanup unused functions declarations from jbd2.h Ritesh Harjani
2022-01-13 11:01 ` Jan Kara
2022-01-13 3:26 ` [PATCH 5/6] jbd2: Refactor wait logic for transaction updates into a common function Ritesh Harjani
2022-01-13 11:30 ` Jan Kara
2022-01-13 12:17 ` Ritesh Harjani
2022-01-13 3:26 ` [PATCH 6/6] jbd2: No need to use t_handle_lock in jbd2_journal_wait_updates Ritesh Harjani
2022-01-13 11:27 ` Jan Kara [this message]
2022-01-13 12:38 ` Ritesh Harjani
2022-01-17 12:55 ` Ritesh Harjani
2022-01-17 14:38 ` Jan Kara
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