Date:	Thu, 3 Oct 2013 10:05:26 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	T Makphaibulchoke <tmac@...com>
Cc:	tytso@....edu, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	aswin@...com, aswin_proj@...ts.hp.com
Subject: Re: [PATCH 2/2] fs/ext4/namei.c: reducing contention on
 s_orphan_lock mmutex

Hello,

On Wed, Oct 02, 2013 at 09:36:59AM -0600, T Makphaibulchoke wrote:
> Instead of using a single per super block mutex, s_orphan_lock, to serialize
> all orphan list updates, a separate mutex and spinlock are used to
> protect the on disk and in memory orphan lists respecvitely.
> 
> At the same time, a per inode mutex is used to serialize orphan list
> updates of a single inode.
> 
> Signed-off-by: T. Makphaibulchoke <tmac@...com>
> ---
>  fs/ext4/namei.c | 139 ++++++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 100 insertions(+), 39 deletions(-)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 35f55a0..d7d3d0f 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -2554,12 +2554,24 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
>  	struct super_block *sb = inode->i_sb;
>  	struct ext4_iloc iloc;
>  	int err = 0, rc;
> +	struct ext4_inode_info *ext4_inode = EXT4_I(inode);
> +	struct ext4_sb_info *ext4_sb = EXT4_SB(sb);
> +	struct mutex *inode_orphan_mutex;
> +	spinlock_t *orphan_lock;
> +	struct mutex *ondisk_orphan_mutex;
> +	struct list_head *prev;
> +	unsigned int next_inum;
> +	struct inode *next_inode;
>  
> -	if (!EXT4_SB(sb)->s_journal)
> +	if (ext4_sb->s_journal)
        ^^^^^^^^
        typo: !ext4_sb->s_journal
I am not sure whether or not this will impact the result because when
journal is enabled the inode will not be added into orphan list.

Regards,
                                                - Zheng

>  		return 0;
>  
> -	mutex_lock(&EXT4_SB(sb)->s_orphan_lock);
> -	if (!list_empty(&EXT4_I(inode)->i_orphan))
> +	inode_orphan_mutex = &ext4_inode->i_orphan_mutex;
> +	orphan_lock = &ext4_sb->s_orphan_lock;
> +	ondisk_orphan_mutex = &ext4_sb->s_ondisk_orphan_lock;
> +	mutex_lock(inode_orphan_mutex);
> +	prev = ext4_inode->i_orphan.prev;
> +	if (prev != &ext4_inode->i_orphan)
>  		goto out_unlock;
>  
>  	/*
> @@ -2579,17 +2591,28 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
>  	err = ext4_reserve_inode_write(handle, inode, &iloc);
>  	if (err)
>  		goto out_unlock;
> +	mutex_lock(ondisk_orphan_mutex);
>  	/*
>  	 * Due to previous errors inode may be already a part of on-disk
>  	 * orphan list. If so skip on-disk list modification.
>  	 */
>  	if (NEXT_ORPHAN(inode) && NEXT_ORPHAN(inode) <=
> -		(le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count)))
> +		(le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count))) {
> +			mutex_unlock(ondisk_orphan_mutex);
>  			goto mem_insert;
> +	}
>  
>  	/* Insert this inode at the head of the on-disk orphan list... */
> -	NEXT_ORPHAN(inode) = le32_to_cpu(EXT4_SB(sb)->s_es->s_last_orphan);
> -	EXT4_SB(sb)->s_es->s_last_orphan = cpu_to_le32(inode->i_ino);
> +	next_inum = le32_to_cpu(EXT4_SB(sb)->s_es->s_last_orphan);
> +	NEXT_ORPHAN(inode) = next_inum;
> +	next_inode = ilookup(sb, next_inum);
> +	if (next_inode)
> +		EXT4_I(next_inode)->i_prev_orphan = inode->i_ino;
> +	ext4_sb->s_es->s_last_orphan = cpu_to_le32(inode->i_ino);
> +	ext4_inode->i_prev_orphan = 0;
> +	mutex_unlock(ondisk_orphan_mutex);
> +	if (next_inode)
> +		iput(next_inode);
>  	err = ext4_handle_dirty_super(handle, sb);
>  	rc = ext4_mark_iloc_dirty(handle, inode, &iloc);
>  	if (!err)
> @@ -2604,14 +2627,17 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
>  	 * This is safe: on error we're going to ignore the orphan list
>  	 * anyway on the next recovery. */
>  mem_insert:
> -	if (!err)
> -		list_add(&EXT4_I(inode)->i_orphan, &EXT4_SB(sb)->s_orphan);
> +	if (!err) {
> +		spin_lock(orphan_lock);
> +		list_add(&ext4_inode->i_orphan, &ext4_sb->s_orphan);
> +		spin_unlock(orphan_lock);
> +	}
>  
>  	jbd_debug(4, "superblock will point to %lu\n", inode->i_ino);
>  	jbd_debug(4, "orphan inode %lu will point to %d\n",
>  			inode->i_ino, NEXT_ORPHAN(inode));
>  out_unlock:
> -	mutex_unlock(&EXT4_SB(sb)->s_orphan_lock);
> +	mutex_unlock(inode_orphan_mutex);
>  	ext4_std_error(inode->i_sb, err);
>  	return err;
>  }
> @@ -2624,71 +2650,106 @@ int ext4_orphan_del(handle_t *handle, struct inode *inode)
>  {
>  	struct list_head *prev;
>  	struct ext4_inode_info *ei = EXT4_I(inode);
> -	struct ext4_sb_info *sbi;
> +	struct inode *i_next = NULL;
> +	struct inode *i_prev = NULL;
> +	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>  	__u32 ino_next;
> +	unsigned int ino_prev;
>  	struct ext4_iloc iloc;
>  	int err = 0;
> +	struct mutex *inode_orphan_mutex;
> +	spinlock_t *orphan_lock;
> +	struct mutex *ondisk_orphan_mutex;
>  
> -	if ((!EXT4_SB(inode->i_sb)->s_journal) &&
> -	    !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS))
> +	if ((!sbi->s_journal) &&
> +	    !(sbi->s_mount_state & EXT4_ORPHAN_FS))
>  		return 0;
>  
> -	mutex_lock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
> -	if (list_empty(&ei->i_orphan))
> -		goto out;
> -
> -	ino_next = NEXT_ORPHAN(inode);
> +	inode_orphan_mutex = &ei->i_orphan_mutex;
> +	orphan_lock = &sbi->s_orphan_lock;
> +	ondisk_orphan_mutex = &sbi->s_ondisk_orphan_lock;
> +	mutex_lock(inode_orphan_mutex);
>  	prev = ei->i_orphan.prev;
> -	sbi = EXT4_SB(inode->i_sb);
> +	if (prev == &ei->i_orphan) {
> +		mutex_unlock(inode_orphan_mutex);
> +		return err;
> +	}
>  
>  	jbd_debug(4, "remove inode %lu from orphan list\n", inode->i_ino);
>  
> +	spin_lock(orphan_lock);
>  	list_del_init(&ei->i_orphan);
> +	spin_unlock(orphan_lock);
>  
>  	/* If we're on an error path, we may not have a valid
>  	 * transaction handle with which to update the orphan list on
>  	 * disk, but we still need to remove the inode from the linked
>  	 * list in memory. */
> -	if (!handle)
> -		goto out;
> +	if (!handle) {
> +		mutex_unlock(inode_orphan_mutex);
> +		return err;
> +	}
>  
>  	err = ext4_reserve_inode_write(handle, inode, &iloc);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(inode_orphan_mutex);
>  		goto out_err;
> +	}
>  
> -	if (prev == &sbi->s_orphan) {
> +	mutex_lock(ondisk_orphan_mutex);
> +	ino_next = NEXT_ORPHAN(inode);
> +	if (ino_next > 0) {
> +		i_next = ilookup(inode->i_sb, ino_next);
> +		assert(i_next);
> +	}
> +	ino_prev = ei->i_prev_orphan;
> +	if (!ino_prev) {
>  		jbd_debug(4, "superblock will point to %u\n", ino_next);
>  		BUFFER_TRACE(sbi->s_sbh, "get_write_access");
>  		err = ext4_journal_get_write_access(handle, sbi->s_sbh);
> -		if (err)
> -			goto out_brelse;
> -		sbi->s_es->s_last_orphan = cpu_to_le32(ino_next);
> -		err = ext4_handle_dirty_super(handle, inode->i_sb);
> +		if (!err) {
> +			sbi->s_es->s_last_orphan = cpu_to_le32(ino_next);
> +			if (i_next)
> +				EXT4_I(i_next)->i_prev_orphan = 0;
> +		}
> +		mutex_unlock(ondisk_orphan_mutex);
> +		if (!err)
> +			err = ext4_handle_dirty_super(handle, inode->i_sb);
>  	} else {
>  		struct ext4_iloc iloc2;
> -		struct inode *i_prev =
> -			&list_entry(prev, struct ext4_inode_info, i_orphan)->vfs_inode;
> -
> -		jbd_debug(4, "orphan inode %lu will point to %u\n",
> -			  i_prev->i_ino, ino_next);
> -		err = ext4_reserve_inode_write(handle, i_prev, &iloc2);
> -		if (err)
> -			goto out_brelse;
> -		NEXT_ORPHAN(i_prev) = ino_next;
> -		err = ext4_mark_iloc_dirty(handle, i_prev, &iloc2);
> +		i_prev = ilookup(inode->i_sb, ino_prev);
> +
> +		assert(i_prev);
> +		if (i_prev) {
> +			jbd_debug(4, "orphan inode %lu will point to %u\n",
> +				i_prev->i_ino, ino_next);
> +			err = ext4_reserve_inode_write(handle, i_prev, &iloc2);
> +		} else
> +			err = -ENOENT;
> +		if (!err) {
> +			NEXT_ORPHAN(i_prev) = ino_next;
> +			if (i_next)
> +				EXT4_I(i_next)->i_prev_orphan = ino_prev;
> +		}
> +		mutex_unlock(ondisk_orphan_mutex);
> +		if (i_prev && !err)
> +			err = ext4_mark_iloc_dirty(handle, i_prev, &iloc2);
>  	}
>  	if (err)
>  		goto out_brelse;
>  	NEXT_ORPHAN(inode) = 0;
> +	mutex_unlock(inode_orphan_mutex);
>  	err = ext4_mark_iloc_dirty(handle, inode, &iloc);
> -
>  out_err:
> +	if (i_next)
> +		iput(i_next);
> +	if (i_prev)
> +		iput(i_prev);
>  	ext4_std_error(inode->i_sb, err);
> -out:
> -	mutex_unlock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
>  	return err;
>  
>  out_brelse:
> +	mutex_unlock(inode_orphan_mutex);
>  	brelse(iloc.bh);
>  	goto out_err;
>  }
> -- 
> 1.7.11.3
> 
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