Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range

From: Ross Zwisler
Date: Tue Aug 30 2016 - 18:01:49 EST

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:

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

My usage fits well with the current implementation of the radix tree, and I'd
like to keep it simple if I can.