Re: [PATCH 1/5] maple_tree: Allow external locks to be configured with their map

[Mark Brown <broonie@kernel.org>]

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On Thu, Aug 22, 2024 at 08:55:20PM +0100, Matthew Wilcox wrote:
> On Thu, Aug 22, 2024 at 08:48:56PM +0100, Mark Brown wrote:

> > I mean, we do use the internal lock here since otherwise lockdep moans
> > but it's pure overhead which just complicates the code.  It's only ever

> When it's an uncontended spinlock, there's really no overhead.  I wish I'd
> been firmer on that point earlier and prohibited the external lock hack.

> The point is that the lock protects the tree.  If we are ever going to
> be able to defragment slabs (and I believe this is an ability that Linux
> must gain), we must be able to go from the object (the maple node) to
> a lock that will let us reallocate the node.  If there's some external
> lock that protects the tree, we can't possibly do that.

If the external lock guarantees that nothing can possibly be contending
access to the tree (including the read side) I don't see any issue
there?

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