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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