On Fri, May 18, 2018 at 01:08:08PM +0200, Peter Zijlstra wrote: > On Fri, May 18, 2018 at 06:18:04AM -0400, Kent Overstreet wrote: > > On Fri, May 18, 2018 at 11:52:04AM +0200, Peter Zijlstra wrote: > > > On Fri, May 18, 2018 at 03:49:06AM -0400, Kent Overstreet wrote: > > > > > > No.. and most certainly not without a _very_ good reason. > > > > Ok, can I ask why? > > Because it is an internal helper for lock implementations that want to > do optimistic spinning, it isn't a lock on its own and lacks several > things you would expect. > > Using it is tricky and I don't trust random module authors to get 1+1 > right, let alone use this thing correctly (no judgement on your code, > just in general). Yeah, that's true. I just modelled my usage on the rwsem code. It does strike me that the whole optimistic spin algorithm (mutex_optimistic_spin() and rwsem_optimistic_spin()) are ripe for factoring out. They've been growing more optimizations I see, and the optimizations mostly aren't specific to either locks. > > Here's what it's for: > > I'll try and have a look soon :-) But does that really _have_ to live in > a module? No, I'd be completely fine with moving six locks out of bcachefs, just don't know that there'd be any other users. But I suppose we do have other filesystems that use btrees, and that's what they're for.
