[PATCH] btrfs: Remove btrfs_inode::delayed_iput_count

[PATCH] btrfs: Remove btrfs_inode::delayed_iput_count

[Nikolay Borisov]

delayed_iput_count wa supposed to be used to implement, well, delayed
iput. The idea is that we keep accumulating the number of iputs we do
until eventually the inode is deleted. Turns out we never really
switched the delayed_iput_count from 0 to 1, hence all conditional
code relying on the value of that member being different than 0 was
never executed. This, as it turns out, didn't cause any problem due
to the simple fact that the generic inode's i_count member was always
used to count the number of iputs. So let's just remove the unused
member and all unused code. This patch essentially provides no
functional changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/btrfs_inode.h |  1 -
 fs/btrfs/inode.c       | 17 +++--------------
 2 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 63f0ccc92a71..f527e99c9f8d 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -195,7 +195,6 @@ struct btrfs_inode {
 
 	/* Hook into fs_info->delayed_iputs */
 	struct list_head delayed_iput;
-	long delayed_iput_count;
 
 	/*
 	 * To avoid races between lockless (i_mutex not held) direct IO writes
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 029399593049..2225f613516c 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3252,12 +3252,8 @@ void btrfs_add_delayed_iput(struct inode *inode)
 		return;
 
 	spin_lock(&fs_info->delayed_iput_lock);
-	if (binode->delayed_iput_count == 0) {
-		ASSERT(list_empty(&binode->delayed_iput));
-		list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
-	} else {
-		binode->delayed_iput_count++;
-	}
+	ASSERT(list_empty(&binode->delayed_iput));
+	list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
 	spin_unlock(&fs_info->delayed_iput_lock);
 }
 
@@ -3270,13 +3266,7 @@ void btrfs_run_delayed_iputs(struct btrfs_fs_info *fs_info)
 
 		inode = list_first_entry(&fs_info->delayed_iputs,
 				struct btrfs_inode, delayed_iput);
-		if (inode->delayed_iput_count) {
-			inode->delayed_iput_count--;
-			list_move_tail(&inode->delayed_iput,
-					&fs_info->delayed_iputs);
-		} else {
-			list_del_init(&inode->delayed_iput);
-		}
+		list_del_init(&inode->delayed_iput);
 		spin_unlock(&fs_info->delayed_iput_lock);
 		iput(&inode->vfs_inode);
 		spin_lock(&fs_info->delayed_iput_lock);
@@ -9424,7 +9414,6 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 	ei->dir_index = 0;
 	ei->last_unlink_trans = 0;
 	ei->last_log_commit = 0;
-	ei->delayed_iput_count = 0;
 
 	spin_lock_init(&ei->lock);
 	ei->outstanding_extents = 0;
-- 
2.7.4

Re: [PATCH] btrfs: Remove btrfs_inode::delayed_iput_count

[Edmund Nadolski]

On 01/15/2018 05:31 AM, Nikolay Borisov wrote:
> delayed_iput_count wa supposed to be used to implement, well, delayed
> iput. The idea is that we keep accumulating the number of iputs we do
> until eventually the inode is deleted. Turns out we never really
> switched the delayed_iput_count from 0 to 1, hence all conditional
> code relying on the value of that member being different than 0 was
> never executed. This, as it turns out, didn't cause any problem due
> to the simple fact that the generic inode's i_count member was always
> used to count the number of iputs. So let's just remove the unused
> member and all unused code. This patch essentially provides no
> functional changes.
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>

Since the 8089fe62c6 changelog mentions the need for a count, it might
be nice to include a brief code comment about the i_count effect.

Reviewed-by: Edmund Nadolski <enadolski@suse.com>


> ---
>  fs/btrfs/btrfs_inode.h |  1 -
>  fs/btrfs/inode.c       | 17 +++--------------
>  2 files changed, 3 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> index 63f0ccc92a71..f527e99c9f8d 100644
> --- a/fs/btrfs/btrfs_inode.h
> +++ b/fs/btrfs/btrfs_inode.h
> @@ -195,7 +195,6 @@ struct btrfs_inode {
>  
>  	/* Hook into fs_info->delayed_iputs */
>  	struct list_head delayed_iput;
> -	long delayed_iput_count;
>  
>  	/*
>  	 * To avoid races between lockless (i_mutex not held) direct IO writes
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 029399593049..2225f613516c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -3252,12 +3252,8 @@ void btrfs_add_delayed_iput(struct inode *inode)
>  		return;
>  
>  	spin_lock(&fs_info->delayed_iput_lock);
> -	if (binode->delayed_iput_count == 0) {
> -		ASSERT(list_empty(&binode->delayed_iput));
> -		list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
> -	} else {
> -		binode->delayed_iput_count++;
> -	}
> +	ASSERT(list_empty(&binode->delayed_iput));
> +	list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
>  	spin_unlock(&fs_info->delayed_iput_lock);
>  }
>  
> @@ -3270,13 +3266,7 @@ void btrfs_run_delayed_iputs(struct btrfs_fs_info *fs_info)
>  
>  		inode = list_first_entry(&fs_info->delayed_iputs,
>  				struct btrfs_inode, delayed_iput);
> -		if (inode->delayed_iput_count) {
> -			inode->delayed_iput_count--;
> -			list_move_tail(&inode->delayed_iput,
> -					&fs_info->delayed_iputs);
> -		} else {
> -			list_del_init(&inode->delayed_iput);
> -		}
> +		list_del_init(&inode->delayed_iput);
>  		spin_unlock(&fs_info->delayed_iput_lock);
>  		iput(&inode->vfs_inode);
>  		spin_lock(&fs_info->delayed_iput_lock);
> @@ -9424,7 +9414,6 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
>  	ei->dir_index = 0;
>  	ei->last_unlink_trans = 0;
>  	ei->last_log_commit = 0;
> -	ei->delayed_iput_count = 0;
>  
>  	spin_lock_init(&ei->lock);
>  	ei->outstanding_extents = 0;
> 

Re: [PATCH] btrfs: Remove btrfs_inode::delayed_iput_count

[David Sterba]

On Mon, Jan 15, 2018 at 10:16:54AM -0700, Edmund Nadolski wrote:
> 
> 
> On 01/15/2018 05:31 AM, Nikolay Borisov wrote:
> > delayed_iput_count wa supposed to be used to implement, well, delayed
> > iput. The idea is that we keep accumulating the number of iputs we do
> > until eventually the inode is deleted. Turns out we never really
> > switched the delayed_iput_count from 0 to 1, hence all conditional
> > code relying on the value of that member being different than 0 was
> > never executed. This, as it turns out, didn't cause any problem due
> > to the simple fact that the generic inode's i_count member was always
> > used to count the number of iputs. So let's just remove the unused
> > member and all unused code. This patch essentially provides no
> > functional changes.
> > 
> > Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> 
> Since the 8089fe62c6 changelog mentions the need for a count, it might
> be nice to include a brief code comment about the i_count effect.

Agreed.

> Reviewed-by: Edmund Nadolski <enadolski@suse.com>

Reviewed-by: David Sterba <dsterba@suse.com>

[PATCH v2] btrfs: Remove btrfs_inode::delayed_iput_count

[Nikolay Borisov]

delayed_iput_count wa supposed to be used to implement, well, delayed
iput. The idea is that we keep accumulating the number of iputs we do
until eventually the inode is deleted. Turns out we never really
switched the delayed_iput_count from 0 to 1, hence all conditional
code relying on the value of that member being different than 0 was
never executed. This, as it turns out, didn't cause any problem due
to the simple fact that the generic inode's i_count member was always
used to count the number of iputs. So let's just remove the unused
member and all unused code. This patch essentially provides no
functional changes. While at it, also add proper documentation for 
btrfs_add_delayed_iput 

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
v2: Add function documentation to make it clear how delayed_iput works and 
uses vfs_inode::i_count

 fs/btrfs/btrfs_inode.h |  1 -
 fs/btrfs/inode.c       | 26 ++++++++++++--------------
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 63f0ccc92a71..f527e99c9f8d 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -195,7 +195,6 @@ struct btrfs_inode {
 
 	/* Hook into fs_info->delayed_iputs */
 	struct list_head delayed_iput;
-	long delayed_iput_count;
 
 	/*
 	 * To avoid races between lockless (i_mutex not held) direct IO writes
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 029399593049..7f568b05b8fd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3243,6 +3243,15 @@ static int btrfs_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
 				      start, (size_t)(end - start + 1));
 }
 
+/* btrfs_add_delayed_iput - perform a delayed iput on @inode
+ *
+ * @inode: The inode we want to perform iput on
+ *
+ * This function uses the generic vfs_inode::i_count to track whether we
+ * should just decrement it (in case it's > 1) or if this is the last
+ * iput then link the inode to the delayed iput machinery. Delayed iputs
+ * are processed at transaction commit time/superblock commit/cleaner kthread
+ */
 void btrfs_add_delayed_iput(struct inode *inode)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
@@ -3252,12 +3261,8 @@ void btrfs_add_delayed_iput(struct inode *inode)
 		return;
 
 	spin_lock(&fs_info->delayed_iput_lock);
-	if (binode->delayed_iput_count == 0) {
-		ASSERT(list_empty(&binode->delayed_iput));
-		list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
-	} else {
-		binode->delayed_iput_count++;
-	}
+	ASSERT(list_empty(&binode->delayed_iput));
+	list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
 	spin_unlock(&fs_info->delayed_iput_lock);
 }
 
@@ -3270,13 +3275,7 @@ void btrfs_run_delayed_iputs(struct btrfs_fs_info *fs_info)
 
 		inode = list_first_entry(&fs_info->delayed_iputs,
 				struct btrfs_inode, delayed_iput);
-		if (inode->delayed_iput_count) {
-			inode->delayed_iput_count--;
-			list_move_tail(&inode->delayed_iput,
-					&fs_info->delayed_iputs);
-		} else {
-			list_del_init(&inode->delayed_iput);
-		}
+		list_del_init(&inode->delayed_iput);
 		spin_unlock(&fs_info->delayed_iput_lock);
 		iput(&inode->vfs_inode);
 		spin_lock(&fs_info->delayed_iput_lock);
@@ -9424,7 +9423,6 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 	ei->dir_index = 0;
 	ei->last_unlink_trans = 0;
 	ei->last_log_commit = 0;
-	ei->delayed_iput_count = 0;
 
 	spin_lock_init(&ei->lock);
 	ei->outstanding_extents = 0;
-- 
2.7.4

Re: [PATCH v2] btrfs: Remove btrfs_inode::delayed_iput_count

[David Sterba]

On Tue, Jan 16, 2018 at 09:31:58AM +0200, Nikolay Borisov wrote:
> delayed_iput_count wa supposed to be used to implement, well, delayed
> iput. The idea is that we keep accumulating the number of iputs we do
> until eventually the inode is deleted. Turns out we never really
> switched the delayed_iput_count from 0 to 1, hence all conditional
> code relying on the value of that member being different than 0 was
> never executed. This, as it turns out, didn't cause any problem due
> to the simple fact that the generic inode's i_count member was always
> used to count the number of iputs. So let's just remove the unused
> member and all unused code. This patch essentially provides no
> functional changes. While at it, also add proper documentation for 
> btrfs_add_delayed_iput 
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>

Reviewed-by: David Sterba <dsterba@suse.com>