On Mon, Aug 29, 2016 at 06:52:54PM +0000, Matthew Wilcox wrote: > It may be protected by the mapping lock in the current code, but I would it > expect it to become an RCU lookup + lock eventually. No mapping lock, just > like the page cache. > > Even if we can work around it, why do we want to? What's the compelling > reason to change from the current radix tree representation of order-N > entries to an arbitrary range? There are no in-kernel users right now; is > there a performance reason to change? We don't usually change an API in > anticipation of future users appearing, particularly when the API makes it > harder for the existing users to use it.
I do have a patch set out for review which uses the multi-order nature of the radix tree: https://lkml.org/lkml/2016/8/23/725 This code takes advantage of the fact that using the radix tree for an order-0 entry is the same as for a multi-order entry. Both have a single lock bit, and a single entry that i need to use for lookups, sets, locking and unlocking. My usage fits well with the current implementation of the radix tree, and I'd like to keep it simple if I can.
