Messages in this thread | | | Date | Mon, 13 Apr 2009 21:44:35 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 1/3] radix-tree: add radix_tree_prev_hole() |
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On Sun, Apr 12, 2009 at 10:29:52AM -0700, Andrew Morton wrote: > On Sun, 12 Apr 2009 15:19:51 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote: > > > +unsigned long radix_tree_prev_hole(struct radix_tree_root *root, > > + unsigned long index, unsigned long max_scan) > > +{ > > + unsigned long i; > > + > > + for (i = 0; i < max_scan; i++) { > > + if (!radix_tree_lookup(root, index)) > > + break; > > + index--; > > + if (index == LONG_MAX) > > + break; > > + } > > + > > + return index; > > +} > > argh. This is about as inefficient as we could possibly make it :(
Right, a dumb loop!
> Really, this function should dive into radix-tree internals and walk > individual radix_tree_node.slots[] arrays. And heck, it can peek at > radix_tree_node.count and _bypass_ entire nodes, too.
Good idea! In fact I'm planning such a smart version. It will be using radix_tree_lookup_slot() to access the ->count member, in order to check if the whole slot can be bypassed.
radix_tree_next_hole() is another optimization candidate. But that will be a post 2.6.30 stuff.
The current dumb-but-obvious-right version is OK for 2.6.30, because in most radix_tree_prev_hole() invocations the actual loop count will be merely 1.
Thanks, Fengguang
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