[ruby-core:42457] [ruby-trunk - Feature #5903] Optimize st_table (take 2)

Issue #5903 has been updated by Yura Sokolov.


I've updated `table packing` patch to correlate with trunk
https://github.com/ruby/ruby/pull/84
https://github.com/ruby/ruby/pull/84.patch

Also there is additional commit which increases usage of `st_foreach_nocheck` 
https://github.com/funny-falcon/ruby/commit/95d6ddcb2b91
https://github.com/funny-falcon/ruby/commit/95d6ddcb2b91.diff
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Feature #5903: Optimize st_table (take 2)
https://bugs.ruby-lang.org/issues/5903

Author: Yura Sokolov
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


Given some of preparations to this patches already merged into ruby-trunk,
I suggest patches for improving st_table second time (first were #5789):

1) Usage of packing for st_table of any kind, not only for numeric hashes.

Most of hashes, allocated during page render in Rails are smaller than 6 entries.
In fact, during rendering "Issues" page of Redmine, 40% of hashes not even grows
above 1 entry. They are small options hashes, passed to numerous helper methods.

This patch packs hashes upto 6 entries in a way like numeric hashes from trunk.
Also it pack hashes of size 0 and 1 into `st_table` inself, so that there is no
need to allocate any "bins" at all.

https://github.com/ruby/ruby/pull/84.patch
https://github.com/ruby/ruby/pull/84

2) Usage of specialized pool for allocating st_table, st_table_entry structures
and st_table.bins of smallest size (11)

Usage of specialized pool for this allocations give great speedup for hash creation.
Also it gives countable reduction of memory consumption.

https://github.com/ruby/ruby/pull/83.patch
https://github.com/ruby/ruby/pull/83

First patch gives little overhead for creating hashes bigger than 6 entries when applied alone.
But both patches combined are not slower than ruby-trunk for hashes of any size.

Performance testing is here https://gist.github.com/1626602


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