linux-kernel - Re: [PATCH 1/6] lib: Implement range locks

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Message-ID: <20130204164142.GG7523@quack.suse.cz>
Date:	Mon, 4 Feb 2013 17:41:42 +0100
From:	Jan Kara <jack@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/6] lib: Implement range locks

On Thu 31-01-13 15:57:26, Andrew Morton wrote:
> On Thu, 31 Jan 2013 22:49:49 +0100
> Jan Kara <jack@...e.cz> wrote:
> 
> > Implement range locking using interval tree.
> > 
> > ...
> >
> > +void range_lock(struct range_lock_tree *tree, struct range_lock *lock)
> > +{
> > +	struct interval_tree_node *node;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&tree->lock, flags);
> > +	node = interval_tree_iter_first(&tree->root, lock->node.start,
> > +					lock->node.last);
> > +	while (node) {
> > +		lock->blocking_ranges++;
> > +		node = interval_tree_iter_next(node, lock->node.start,
> > +					       lock->node.last);
> > +	}
> > +	interval_tree_insert(&lock->node, &tree->root);
> > +	/* Do we need to go to sleep? */
> > +	while (lock->blocking_ranges) {
> > +		lock->task = current;
> > +		__set_current_state(TASK_UNINTERRUPTIBLE);
> > +		spin_unlock_irqrestore(&tree->lock, flags);
> > +		schedule();
> > +		spin_lock_irqsave(&tree->lock, flags);
> > +	}
> > +	spin_unlock_irqrestore(&tree->lock, flags);
> > +}
> >
> > ...
> >
> > +void range_unlock(struct range_lock_tree *tree, struct range_lock *lock)
> > +{
> > +	struct interval_tree_node *node;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&tree->lock, flags);
> > +	interval_tree_remove(&lock->node, &tree->root);
> > +	node = interval_tree_iter_first(&tree->root, lock->node.start,
> > +					lock->node.last);
> > +	while (node) {
> > +		range_lock_unblock((struct range_lock *)node);
> > +		node = interval_tree_iter_next(node, lock->node.start,
> > +					       lock->node.last);
> > +	}
> > +	spin_unlock_irqrestore(&tree->lock, flags);
> > +}
> 
> What are the worst-case interrupt-off durations here?
  Good question. In theory, it could be relatively long, e.g. when there
are lots of DIOs in flight against a range which is locked. I'll do some
measurements to get some idea.
 
> I note that the new exported functions in this patchset are
> refreshingly free of documentation ;)
  They are *so* obvious ;) Point taken... Thanks for review.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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