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From: Nikolay Borisov <nborisov@suse.com>
To: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 1/3] btrfs: switch extent_buffer blocking_writers from atomic to int
Date: Fri, 31 May 2019 11:29:33 +0300	[thread overview]
Message-ID: <ed094516-d79b-0981-5f1e-52002db1d874@suse.com> (raw)
In-Reply-To: <ebba72a9ef564b27fb5f652e3edcfbca3e981a10.1559233731.git.dsterba@suse.com>



On 30.05.19 г. 19:31 ч., David Sterba wrote:
> The blocking_writers is either 0 or 1 and always updated under the lock,
> so we don't need the atomic_t semantics.>
> Signed-off-by: David Sterba <dsterba@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/extent_io.c  |  2 +-
>  fs/btrfs/extent_io.h  |  2 +-
>  fs/btrfs/locking.c    | 46 +++++++++++++++++++------------------------
>  fs/btrfs/print-tree.c |  2 +-
>  4 files changed, 23 insertions(+), 29 deletions(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 2f38c10d2bfb..57b6de9df7c4 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4823,7 +4823,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
>  	eb->bflags = 0;
>  	rwlock_init(&eb->lock);
>  	atomic_set(&eb->blocking_readers, 0);
> -	atomic_set(&eb->blocking_writers, 0);
> +	eb->blocking_writers = 0;
>  	eb->lock_nested = false;
>  	init_waitqueue_head(&eb->write_lock_wq);
>  	init_waitqueue_head(&eb->read_lock_wq);
> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
> index aa18a16a6ed7..201da61dfc21 100644
> --- a/fs/btrfs/extent_io.h
> +++ b/fs/btrfs/extent_io.h
> @@ -167,7 +167,7 @@ struct extent_buffer {
>  	struct rcu_head rcu_head;
>  	pid_t lock_owner;
>  
> -	atomic_t blocking_writers;
> +	int blocking_writers;
>  	atomic_t blocking_readers;
>  	bool lock_nested;
>  	/* >= 0 if eb belongs to a log tree, -1 otherwise */
> diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
> index 2f6c3c7851ed..5feb01147e19 100644
> --- a/fs/btrfs/locking.c
> +++ b/fs/btrfs/locking.c
> @@ -111,10 +111,10 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
>  	 */
>  	if (eb->lock_nested && current->pid == eb->lock_owner)
>  		return;
> -	if (atomic_read(&eb->blocking_writers) == 0) {
> +	if (eb->blocking_writers == 0) {
>  		btrfs_assert_spinning_writers_put(eb);
>  		btrfs_assert_tree_locked(eb);
> -		atomic_inc(&eb->blocking_writers);
> +		eb->blocking_writers++;
>  		write_unlock(&eb->lock);
>  	}
>  }
> @@ -148,12 +148,11 @@ void btrfs_clear_lock_blocking_write(struct extent_buffer *eb)
>  	 */
>  	if (eb->lock_nested && current->pid == eb->lock_owner)
>  		return;
> -	BUG_ON(atomic_read(&eb->blocking_writers) != 1);
>  	write_lock(&eb->lock);
> +	BUG_ON(eb->blocking_writers != 1);
>  	btrfs_assert_spinning_writers_get(eb);
> -	/* atomic_dec_and_test implies a barrier */
> -	if (atomic_dec_and_test(&eb->blocking_writers))
> -		cond_wake_up_nomb(&eb->write_lock_wq);
> +	if (--eb->blocking_writers == 0)
> +		cond_wake_up(&eb->write_lock_wq);
>  }
>  
>  /*
> @@ -167,12 +166,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb)
>  	if (trace_btrfs_tree_read_lock_enabled())
>  		start_ns = ktime_get_ns();
>  again:
> -	BUG_ON(!atomic_read(&eb->blocking_writers) &&
> -	       current->pid == eb->lock_owner);
> -
>  	read_lock(&eb->lock);
> -	if (atomic_read(&eb->blocking_writers) &&
> -	    current->pid == eb->lock_owner) {
> +	BUG_ON(eb->blocking_writers == 0 &&
> +	       current->pid == eb->lock_owner);
> +	if (eb->blocking_writers && current->pid == eb->lock_owner) {
>  		/*
>  		 * This extent is already write-locked by our thread. We allow
>  		 * an additional read lock to be added because it's for the same
> @@ -185,10 +182,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb)
>  		trace_btrfs_tree_read_lock(eb, start_ns);
>  		return;
>  	}
> -	if (atomic_read(&eb->blocking_writers)) {
> +	if (eb->blocking_writers) {
>  		read_unlock(&eb->lock);
>  		wait_event(eb->write_lock_wq,
> -			   atomic_read(&eb->blocking_writers) == 0);
> +			   eb->blocking_writers == 0);
>  		goto again;
>  	}
>  	btrfs_assert_tree_read_locks_get(eb);
> @@ -203,11 +200,11 @@ void btrfs_tree_read_lock(struct extent_buffer *eb)
>   */
>  int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
>  {
> -	if (atomic_read(&eb->blocking_writers))
> +	if (eb->blocking_writers)
>  		return 0;
>  
>  	read_lock(&eb->lock);
> -	if (atomic_read(&eb->blocking_writers)) {
> +	if (eb->blocking_writers) {
>  		read_unlock(&eb->lock);
>  		return 0;
>  	}
> @@ -223,13 +220,13 @@ int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
>   */
>  int btrfs_try_tree_read_lock(struct extent_buffer *eb)
>  {
> -	if (atomic_read(&eb->blocking_writers))
> +	if (eb->blocking_writers)
>  		return 0;
>  
>  	if (!read_trylock(&eb->lock))
>  		return 0;
>  
> -	if (atomic_read(&eb->blocking_writers)) {
> +	if (eb->blocking_writers) {
>  		read_unlock(&eb->lock);
>  		return 0;
>  	}
> @@ -245,13 +242,11 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb)
>   */
>  int btrfs_try_tree_write_lock(struct extent_buffer *eb)
>  {
> -	if (atomic_read(&eb->blocking_writers) ||
> -	    atomic_read(&eb->blocking_readers))
> +	if (eb->blocking_writers || atomic_read(&eb->blocking_readers))
>  		return 0;
>  
>  	write_lock(&eb->lock);
> -	if (atomic_read(&eb->blocking_writers) ||
> -	    atomic_read(&eb->blocking_readers)) {
> +	if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) {
>  		write_unlock(&eb->lock);
>  		return 0;
>  	}
> @@ -322,10 +317,9 @@ void btrfs_tree_lock(struct extent_buffer *eb)
>  	WARN_ON(eb->lock_owner == current->pid);
>  again:
>  	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
> -	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
> +	wait_event(eb->write_lock_wq, eb->blocking_writers == 0);
>  	write_lock(&eb->lock);
> -	if (atomic_read(&eb->blocking_readers) ||
> -	    atomic_read(&eb->blocking_writers)) {
> +	if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) {
>  		write_unlock(&eb->lock);
>  		goto again;
>  	}
> @@ -340,7 +334,7 @@ void btrfs_tree_lock(struct extent_buffer *eb)
>   */
>  void btrfs_tree_unlock(struct extent_buffer *eb)
>  {
> -	int blockers = atomic_read(&eb->blocking_writers);
> +	int blockers = eb->blocking_writers;
>  
>  	BUG_ON(blockers > 1);
>  
> @@ -351,7 +345,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
>  
>  	if (blockers) {
>  		btrfs_assert_no_spinning_writers(eb);
> -		atomic_dec(&eb->blocking_writers);
> +		eb->blocking_writers--;
>  		/* Use the lighter barrier after atomic */
>  		smp_mb__after_atomic();
>  		cond_wake_up_nomb(&eb->write_lock_wq);
> diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
> index 1141ca5fae6a..7cb4f1fbe043 100644
> --- a/fs/btrfs/print-tree.c
> +++ b/fs/btrfs/print-tree.c
> @@ -155,7 +155,7 @@ static void print_eb_refs_lock(struct extent_buffer *eb)
>  "refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u",
>  		   atomic_read(&eb->refs), atomic_read(&eb->write_locks),
>  		   atomic_read(&eb->read_locks),
> -		   atomic_read(&eb->blocking_writers),
> +		   eb->blocking_writers,
>  		   atomic_read(&eb->blocking_readers),
>  		   atomic_read(&eb->spinning_writers),
>  		   atomic_read(&eb->spinning_readers),
> 

  reply	other threads:[~2019-05-31  8:29 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-30 16:30 [PATCH 0/3] Extent buffer lock cleanups David Sterba
2019-05-30 16:31 ` [PATCH 1/3] btrfs: switch extent_buffer blocking_writers from atomic to int David Sterba
2019-05-31  8:29   ` Nikolay Borisov [this message]
2019-05-30 16:31 ` [PATCH 2/3] btrfs: switch extent_buffer spinning_writers " David Sterba
2019-05-31  9:19   ` Nikolay Borisov
2019-05-31 11:28     ` David Sterba
2019-05-30 16:31 ` [PATCH 3/3] btrfs: switch extent_buffer write_locks " David Sterba
2019-05-31  9:20   ` Nikolay Borisov
2019-06-07 13:31 ` [PATCH 0/3] Extent buffer lock cleanups David Sterba

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