Re: [PATCH v1 08/11] locks: convert fl_link to a hlist_node

["J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>]

On Fri, May 31, 2013 at 11:07:31PM -0400, Jeff Layton wrote:
> Testing has shown that iterating over the blocked_list for deadlock
> detection turns out to be a bottleneck. In order to alleviate that,
> begin the process of turning it into a hashtable. We start by turning
> the fl_link into a hlist_node and the global lists into hlists. A later
> patch will do the conversion of the blocked_list to a hashtable.

Even simpler would be if we could add a pointer to the (well, a) lock
that a lockowner is blocking on, and then we'd just have to follow a
pointer.  I haven't thought that through, though, perhaps that's hard ot
make work....

--b.

> 
> Signed-off-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  fs/locks.c         |   32 ++++++++++++++++----------------
>  include/linux/fs.h |    2 +-
>  2 files changed, 17 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index fc35b9e..5ed056b 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -163,8 +163,8 @@ int lease_break_time = 45;
>  #define for_each_lock(inode, lockp) \
>  	for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)
>  
> -static LIST_HEAD(file_lock_list);
> -static LIST_HEAD(blocked_list);
> +static HLIST_HEAD(file_lock_list);
> +static HLIST_HEAD(blocked_list);
>  
>  /* Protects the two list heads above */
>  static DEFINE_SPINLOCK(file_lock_lock);
> @@ -173,7 +173,7 @@ static struct kmem_cache *filelock_cache __read_mostly;
>  
>  static void locks_init_lock_heads(struct file_lock *fl)
>  {
> -	INIT_LIST_HEAD(&fl->fl_link);
> +	INIT_HLIST_NODE(&fl->fl_link);
>  	INIT_LIST_HEAD(&fl->fl_block);
>  	init_waitqueue_head(&fl->fl_wait);
>  }
> @@ -207,7 +207,7 @@ void locks_free_lock(struct file_lock *fl)
>  {
>  	BUG_ON(waitqueue_active(&fl->fl_wait));
>  	BUG_ON(!list_empty(&fl->fl_block));
> -	BUG_ON(!list_empty(&fl->fl_link));
> +	BUG_ON(!hlist_unhashed(&fl->fl_link));
>  
>  	locks_release_private(fl);
>  	kmem_cache_free(filelock_cache, fl);
> @@ -486,7 +486,7 @@ static inline void
>  locks_insert_global_blocked(struct file_lock *waiter)
>  {
>  	spin_lock(&file_lock_lock);
> -	list_add(&waiter->fl_link, &blocked_list);
> +	hlist_add_head(&waiter->fl_link, &blocked_list);
>  	spin_unlock(&file_lock_lock);
>  }
>  
> @@ -494,7 +494,7 @@ static inline void
>  locks_delete_global_blocked(struct file_lock *waiter)
>  {
>  	spin_lock(&file_lock_lock);
> -	list_del_init(&waiter->fl_link);
> +	hlist_del_init(&waiter->fl_link);
>  	spin_unlock(&file_lock_lock);
>  }
>  
> @@ -502,7 +502,7 @@ static inline void
>  locks_insert_global_locks(struct file_lock *waiter)
>  {
>  	spin_lock(&file_lock_lock);
> -	list_add_tail(&waiter->fl_link, &file_lock_list);
> +	hlist_add_head(&waiter->fl_link, &file_lock_list);
>  	spin_unlock(&file_lock_lock);
>  }
>  
> @@ -510,7 +510,7 @@ static inline void
>  locks_delete_global_locks(struct file_lock *waiter)
>  {
>  	spin_lock(&file_lock_lock);
> -	list_del_init(&waiter->fl_link);
> +	hlist_del_init(&waiter->fl_link);
>  	spin_unlock(&file_lock_lock);
>  }
>  
> @@ -705,7 +705,7 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
>  {
>  	struct file_lock *fl, *ret = NULL;
>  
> -	list_for_each_entry(fl, &blocked_list, fl_link) {
> +	hlist_for_each_entry(fl, &blocked_list, fl_link) {
>  		if (posix_same_owner(fl, block_fl)) {
>  			ret = fl->fl_next;
>  			if (likely(ret))
> @@ -867,7 +867,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
>  				goto out;
>  			error = FILE_LOCK_DEFERRED;
>  			locks_insert_block(fl, request);
> -			if (list_empty(&request->fl_link))
> +			if (hlist_unhashed(&request->fl_link))
>  				locks_insert_global_blocked(request);
>  			goto out;
>    		}
> @@ -882,10 +882,10 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
>  	 * Now that we know the request is no longer blocked, we can take it
>  	 * off the global list. Some callers send down partially initialized
>  	 * requests, so we only do this if FL_SLEEP is set. Also, avoid taking
> -	 * the lock if the list is empty, as that indicates a request that
> +	 * the lock if the hlist is unhashed, as that indicates a request that
>  	 * never blocked.
>  	 */
> -	if ((request->fl_flags & FL_SLEEP) && !list_empty(&request->fl_link))
> +	if ((request->fl_flags & FL_SLEEP) && !hlist_unhashed(&request->fl_link))
>  		locks_delete_global_blocked(request);
>  
>  	/*
> @@ -2277,11 +2277,11 @@ static int locks_show(struct seq_file *f, void *v)
>  {
>  	struct file_lock *fl, *bfl;
>  
> -	fl = list_entry(v, struct file_lock, fl_link);
> +	fl = hlist_entry(v, struct file_lock, fl_link);
>  
>  	lock_get_status(f, fl, *((loff_t *)f->private), "");
>  
> -	list_for_each_entry(bfl, &blocked_list, fl_link) {
> +	hlist_for_each_entry(bfl, &blocked_list, fl_link) {
>  		if (bfl->fl_next == fl)
>  			lock_get_status(f, bfl, *((loff_t *)f->private), " ->");
>  	}
> @@ -2295,14 +2295,14 @@ static void *locks_start(struct seq_file *f, loff_t *pos)
>  
>  	spin_lock(&file_lock_lock);
>  	*p = (*pos + 1);
> -	return seq_list_start(&file_lock_list, *pos);
> +	return seq_hlist_start(&file_lock_list, *pos);
>  }
>  
>  static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
>  {
>  	loff_t *p = f->private;
>  	++*p;
> -	return seq_list_next(v, &file_lock_list, pos);
> +	return seq_hlist_next(v, &file_lock_list, pos);
>  }
>  
>  static void locks_stop(struct seq_file *f, void *v)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ccb44ea..07a009e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -934,7 +934,7 @@ int locks_in_grace(struct net *);
>   */
>  struct file_lock {
>  	struct file_lock *fl_next;	/* singly linked list for this inode  */
> -	struct list_head fl_link;	/* doubly linked list of all locks */
> +	struct hlist_node fl_link;	/* node in global lists */
>  	struct list_head fl_block;	/* circular list of blocked processes */
>  	fl_owner_t fl_owner;
>  	unsigned int fl_flags;
> -- 
> 1.7.1
>