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

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On Tue, Aug 30, 2016 at 03:21:24PM -0700, Dan Williams wrote:
> On Tue, Aug 30, 2016 at 3:03 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> 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 <mawilcox@microsoft.com> 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.

Perhaps the answer is to have them both?  Matthew's multi-order radix
functionality with siblings for those of us that really *want* a single
canonical entry that we can look up, use tags on, etc.   And Konstantin's
method where we insert a bunch of duplicate entries that don't have sibling
pointers?  Is there a reason why they can't coexist?

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[PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Konstantin Khlebnikov <koct9i@gmail.com> - 2016-08-27 16:20 +0200
  RE: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Matthew Wilcox <mawilcox@microsoft.com> - 2016-08-29 17:40 +0200
    Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Konstantin Khlebnikov <koct9i@gmail.com> - 2016-08-29 18:20 +0200
      Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Konstantin Khlebnikov <koct9i@gmail.com> - 2016-08-29 20:20 +0200
        RE: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Matthew Wilcox <mawilcox@microsoft.com> - 2016-08-29 21:10 +0200
          Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Dan Williams <dan.j.williams@intel.com> - 2016-08-31 00:00 +0200
            Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-08-31 00:10 +0200
              Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Dan Williams <dan.j.williams@intel.com> - 2016-08-31 00:30 +0200
                Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-08-31 01:00 +0200
                Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Konstantin Khlebnikov <koct9i@gmail.com> - 2016-09-01 08:20 +0200
                RE: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Matthew Wilcox <mawilcox@microsoft.com> - 2016-09-02 20:20 +0200
                Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Konstantin Khlebnikov <koct9i@gmail.com> - 2016-09-03 07:00 +0200
                RE: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Matthew Wilcox <mawilcox@microsoft.com> - 2016-08-31 17:00 +0200
                Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Dan Williams <dan.j.williams@intel.com> - 2016-08-31 18:50 +0200
                Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Konstantin Khlebnikov <koct9i@gmail.com> - 2016-09-01 08:20 +0200
          Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-08-31 00:10 +0200
      RE: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Matthew Wilcox <mawilcox@microsoft.com> - 2016-08-29 20:30 +0200
  Re: [PATCH RFC 1/4] lib/radix: add universal radix_tree_fill_range Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-08-31 00:40 +0200

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