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[std-proposals] Flash Alloc - 7x faster
dbj/CPP WG21 STD Proposals
dbj/std-proposals
dbj@dbj.org

Phil Bouchard via Std-Proposals
Attachments
04:23 (7 hours ago)
to std-proposals, Phil

Greetings,

Given the default memory allocator is known to be slow, it came to my attention that if we collect more information at compile-time regarding not only the type being allocated but the container type and the usage frequency then we can have much higher performance.

In the attached example, if we use a queue then we can speed up the overall allocation time by 7x!

Regards,

Phil Bouchard
Founder & CTO
C.: (819) 328-4743

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Phil Bouchard via Std-Proposals
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09:40 (2 hours ago)
to std-proposals, Phil

And here's a more generic one that is 10x faster for straight allocations.

Anyway my point being that apparently the rebind oddity has been removed from the C++20 standards but not from my system headers... So perhaps adding a similar ultra fast allocator such as this one into the stdlib would be constructive.

Regards,
--

Phil Bouchard
Founder & CTO
C.: (819) 328-4743

Flash Alloc

Outputs (10 times faster):    
    new/delete elapsed time: 283698602s
    flashalloc elapsed time: 27572300s
    
    
    Copyright 2021 Phil Bouchard <phil@fornux.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include <iostream>
//#include <cassert>
//#include <cstddef>
#include <chrono>
//#include <tuple>
#include <array>
#include <queue>
#include <list>

using namespace std;

template <typename T, template <typename, typename> class C, size_t S> // type, container type, buffer size based on speed of pre-made benchmark
    struct flashalloc
    {
        typedef T value_type;
        typedef T & reference;
        typedef T const & const_reference;
        typedef size_t size_type;

T * allocate(size_t size)
        {
            if (head.second == page.second->second.end())
            {
                // add a page
                pool.emplace_back();
                
                page.second = -- pool.end();
                head.second = page.second->second.begin();
            }
            
            for (element_t * p = head.second; p != head.second + size; ++ p->first->first, ++ p)
            {
                p->first = -- pool.end();
                p->second = true;
            }
            
            return & head.second->third;
        }
        
        void deallocate(T * o, size_t size)
        {
            element_t * const q = static_cast<element_t *>(static_cast<void *>(static_cast<char *>(static_cast<void *>(o)) - offsetof(element_t, third)));
            
            for (element_t * p = q; p != q + size; -- p->first->first, ++ p)
            {
                p->second = false;
            }

if (q->first->first == 0 && pool.size() > 1)
            {
                // remove a page
                pool.erase(q->first);
            }
        }

private:
        struct page_t;
        
        struct element_t
        {
            typename list<page_t>::iterator first;
            bool second;
            T third;
        };
        
        typedef array<element_t, S * 1024> data_t;
        
        struct page_t
        {
            size_t first;
            data_t second;
        };
        
        list<page_t> pool{1}; // general pool
        
        pair<typename list<page_t>::iterator, typename list<page_t>::iterator> page{make_pair(pool.begin(), pool.begin())}; // begin & end page of the pool
        
        pair<typename data_t::iterator, typename data_t::iterator> head{make_pair(page.first->second.begin(), page.second->second.begin())}; // begin & end in the page        
    };
    
#define LOOP_SIZE 1024 * 1 
#define DATASET_SIZE 0xFF 
    
int main()
{
    {
        auto start = std::chrono::steady_clock::now();
        
        {
            static allocator<int> alloc;
            
            for (size_t i = 0; i < LOOP_SIZE; ++ i)
            {
                int * p = alloc.allocate(DATASET_SIZE);
                alloc.deallocate(p, DATASET_SIZE );
            }
        }
        
        auto end = std::chrono::steady_clock::now();

std::cout << "\nnew/delete elapsed time: " << (end - start).count() << " nanosec\n";
    }
        
    {
        auto start = std::chrono::steady_clock::now();
        
        {
            static flashalloc<int, queue, 1000> alloc;
            
            for (size_t i = 0; i < LOOP_SIZE; ++ i)
            {
                int * p = alloc.allocate(DATASET_SIZE);
                alloc.deallocate(p, DATASET_SIZE );
            }
        }
        
        auto end = std::chrono::steady_clock::now();

std::cout << "\nflashalloc elapsed time: " << (end - start).count() << " nanosec\n";
    }
        
    return 42;
}