On Tue, Aug 30, 2016 at 3:03 PM, Ross Zwisler <[email protected]> wrote: > On Tue, Aug 30, 2016 at 02:56:17PM -0700, Dan Williams wrote: >> On Mon, Aug 29, 2016 at 11:52 AM, Matthew Wilcox <[email protected]> >> 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'd use a fill range api for the radix backing get_dev_pagemap() and >> potentially another use in device-dax. It centralizes the common >> routine of breaking down a range into its constituent power-of-2 >> ranges. > > Does your usage not work with the current sibling & canonical entry model?
It does, but I find myself writing code to walk a range and determine the order of each entry as I insert them. I can see other users needing the same sort of insert helper and the aspect I like of Konstantin's proposed change is that the functionality is part of the core implementation rather than left to be duplicated in each user.
