f36d1d5b89 Use void* throughout support/lockedpool.h (Jeffrey Czyz)
Pull request description:
Replace uses of char* with void* in Arena's member variables. Instead,
cast to char* where needed in the implementation.
Certain compiler environments disallow std::hash<char*> specializations
to prevent hashing the pointer's value instead of the string contents.
Thus, compilation fails when std::unordered_map is keyed by char*.
Explicitly using void* is a workaround in such environments. For
consistency, void* is used throughout all member variables similarly to
the public interface.
Changes to this code are covered by src/test/allocator_tests.cpp.
ACKs for top commit:
achow101:
ACK f36d1d5b89
theStack:
Code-review ACK f36d1d5b89
jonatack:
ACK f36d1d5b89 review, debug build, unit tests, checked clang 15 raises "error: arithmetic on a pointer to void" without the conversions here from the generic void* pointer back to char*
Tree-SHA512: f9074e6d29ef78c795a512a6e00e9b591e2ff34165d09b73eae9eef25098c59e543c194346fcd4e83185a39c430d43744b6f7f9d1728a132843c67bd27ea5189
Replace uses of char* with void* in Arena's member variables. Instead,
cast to char* where needed in the implementation.
Certain compiler environments disallow std::hash<char*> specializations
to prevent hashing the pointer's value instead of the string contents.
Thus, compilation fails when std::unordered_map is keyed by char*.
Explicitly using void* is a workaround in such environments. For
consistency, void* is used throughout all member variables similarly to
the public interface.
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
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 slow O(n) algorithm to O(log(n)) operations. Additionally, some previously O(log(n)) operations are now replaced with O(1) operations by using a hash map. The end effect is that the benchmark runs about 2.5 times faster on my machine:
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.
Use C++11's better capability of expressing an interface of a non-copyable class by publicly deleting its copy ctor and assignment operator instead of just declaring them private.
Add a pool for locked memory chunks, replacing LockedPageManager.
This is something I've been wanting to do for a long time. The current
approach of locking objects where they happen to be on the stack or heap
in-place causes a lot of mlock/munlock system call overhead, slowing
down any handling of keys.
Also locked memory is a limited resource on many operating systems (and
using a lot of it bogs down the system), so the previous approach of
locking every page that may contain any key information (but also other
information) is wasteful.
