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Re: [RFC 00/10] implement alternative and much simpler id allocator

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Hello,

On Fri, Dec 09, 2016 at 02:01:40PM -0800, Andrew Morton wrote:
> On Thu,  8 Dec 2016 02:22:55 +0100 Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:
> 
> > TL;DR: these patches save 250 KB of memory, with more low-hanging
> > fruit ready to pick.
> > 
> > While browsing through the lib/idr.c code, I noticed that the code at
> > the end of ida_get_new_above() probably doesn't work as intended: Most
> > users of ida use it via ida_simple_get(), and that starts by
> > unconditionally calling ida_pre_get(), ensuring that ida->idr has
> > 8==MAX_IDR_FREE idr_layers in its free list id_free. In the common
> > case, none (or at most one) of these get used during
> > ida_get_new_above(), and we only free one, leaving at least 6 (usually
> > 7) idr_layers in the free list.
> 
> Please be aware of
> 
> http://ozlabs.org/~akpm/mmots/broken-out/reimplement-idr-and-ida-using-the-radix-tree.patch
> http://lkml.kernel.org/r/1480369871-5271-68-git-send-email-mawilcox@linuxonhyperv.com
> 
> I expect we'll be merging patches 1-32 of that series into 4.10-rc1 and
> the above patch (#33) into 4.11-rc1.

Ah, yeah, great to see the silly implementation being replaced the
radix tree.  ida_pre_get() looks suspicious tho.  idr_preload()
immedicately being followed by idr_preload_end() probably is broken.
Maybe what we need is moving ida to idr like preload interface and
then convert it to radix based interface?  ida currently assumes
per-ida preloading.

Thanks.

-- 
tejun

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[RFC 00/10] implement alternative and much simpler id allocator Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-08 02:40 +0100
  [RFC 01/10] lib/idr.c: reused free bitmaps are already clear Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-08 02:40 +0100
  [RFC 02/10] lib/idr.c: delete useless condition Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-08 02:40 +0100
  [RFC 09/10] drm: use simpler id allocator Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-08 02:40 +0100
  [RFC 06/10] block: use tida as small id allocator Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-08 02:40 +0100
    Re: [RFC 06/10] block: use tida as small id allocator Jens Axboe <axboe@kernel.dk> - 2016-12-08 05:00 +0100
      Re: [RFC 06/10] block: use tida as small id allocator Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-08 12:20 +0100
  Re: [RFC 00/10] implement alternative and much simpler id allocator Tejun Heo <tj@kernel.org> - 2016-12-09 14:50 +0100
  Re: [RFC 00/10] implement alternative and much simpler id allocator Andrew Morton <akpm@linux-foundation.org> - 2016-12-09 23:10 +0100
    Re: [RFC 00/10] implement alternative and much simpler id allocator Tejun Heo <tj@kernel.org> - 2016-12-12 18:30 +0100
      RE: [RFC 00/10] implement alternative and much simpler id allocator Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-12 18:40 +0100
        Re: [RFC 00/10] implement alternative and much simpler id allocator Tejun Heo <tj@kernel.org> - 2016-12-12 19:10 +0100
    Re: [RFC 00/10] implement alternative and much simpler id allocator Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-16 21:40 +0100
      RE: [RFC 00/10] implement alternative and much simpler id allocator Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-16 22:30 +0100
      RE: [RFC 00/10] implement alternative and much simpler id allocator Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-17 14:30 +0100
        Re: [RFC 00/10] implement alternative and much simpler id allocator Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-12-23 00:50 +0100
          RE: [RFC 00/10] implement alternative and much simpler id allocator Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-23 18:20 +0100
      RE: [RFC 00/10] implement alternative and much simpler id allocator Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-18 03:50 +0100
    RE: [RFC 00/10] implement alternative and much simpler id allocator Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-16 22:50 +0100

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