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Use best-fit strategy in Arena, now O(log(n)) instead O(n)

Authored by Wladimir J. van der Laan <laanwj@gmail.com> on Mar 22 2018, 13:28.

Description

Use best-fit strategy in Arena, now O(log(n)) instead O(n)

Summary:
PR12048:
5fbf7c4 fix nits: variable naming, typos (Martin Ankerl)
1e0ee90 Use best-fit strategy in Arena, now O(log(n)) instead O(n) (Martin Ankerl)

Pull request description:

This replaces the first-fit algorithm used in the Arena with a best-fit. According to "Dynamic Storage Allocation: A Survey and Critical Review", Wilson et. al. 1995, http://www.scs.stanford.edu/14wi-cs140/sched/readings/wilson.pdf, both startegies work well in practice.

The advantage of using best-fit is that we can switch the O(n) allocation to O(log(n)). Additionally, some previously O(log(n)) operations are now O(1) operations by using hash maps. The end effect is that the benchmark runs about 2.5 times faster on my machine:

    # Benchmark, evals, iterations, total, min, max, median
    old: BenchLockedPool, 5, 530, 5.25749, 0.00196938, 0.00199755, 0.00198172
    new: BenchLockedPool, 5, 1300, 5.11313, 0.000781493, 0.000793314, 0.00078606

I've run all unit tests and benchmarks, and increased the number of iterations so that BenchLockedPool takes about 5 seconds again.

Tree-SHA512: 6551e384671f93f10c60df530a29a1954bd265cc305411f665a8756525e5afe2873a8032c797d00b6e8c07e16d9827465d0b662875433147381474a44119ccce

Also included PR16161 which fixes a bug introduced by PR12048:

Changes in #12048 cause a compilation error in Arena::walk() when
ARENA_DEBUG is defined. Specifically, Arena's chunks_free map was
changed to have a different value type.

Additionally, missing includes cause other compilation errors when
ARENA_DEBUG is defined.

Second commit fixes segfault in allocator_tests/arena_tests
The test uses reinterpret_cast<void*> on unallocated memory. Using this
memory in printchunk as char* causes a segfault, so have printchunk take
void* instead.

Reproduced with:

make CPPFLAGS=-DARENA_DEBUG

Backport of Core PR12048 and PR16161
https://github.com/bitcoin/bitcoin/pull/12048/
https://github.com/bitcoin/bitcoin/pull/16161/

Reviewer note: the last commit in PR16161 is TRAVIS related and was therefore modified to our code base.

Test Plan:

make check
test_runner.py
./bitcoin-qt -> settings -> Encrypt Wallet -> set password and/or change password if already encrypted
./bench_bitcoin

old: BenchLockedPool, 5, 530, 5.15069, 0.00192059, 0.00199956, 0.00193796
new: BenchLockedPool, 5, 1300, 4.44411, 0.00067821, 0.000698535, 0.000678916

../configure CPPFLAGS=-DARENA_DEBUG
make check
test_runner.py
ABC_BUILD_NAME=build-asan build-configurations.sh

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3898

Details

Committed
nakihitoJan 9 2020, 18:04
Pushed
nakihitoJan 9 2020, 18:04
Reviewer
Restricted Owners Package
Differential Revision
D3898: Use best-fit strategy in Arena, now O(log(n)) instead O(n)
Parents
rABC4941397cc777: Nits in rpcdump
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