Growing and Shrinking a Pool¶
When sharing a pool between different parts of your application, or even between co-ordinating libraries in the same application, you might want to grow and shrink a pool on demand. By limiting the size of a pool using device memory, you leave more space on the GPU for “unified memory” to move data there.
The basic idea is to create a pool that allocates a block of your minimum size, and then allocate a single word from this pool to ensure the initial block is never freed:
auto pooled_allocator = rm.makeAllocator<umpire::strategy::DynamicPool>(
"GPU_POOL",
allocator,
4ul * 1024ul * 1024ul * 1024ul + 1);
void* hold = pooled_allocator.allocate(64);
UMPIRE_USE_VAR(hold);
To increase the pool size you can preallocate a large chunk and then immediately free it. The pool will retain this memory for use by later allocations:
void* grow = pooled_allocator.allocate( 8ul * 1024ul * 1024ul * 1024ul );
pooled_allocator.deallocate(grow);
Assuming that there are no allocations left in the larger “chunk” of the pool,
you can shrink the pool back down to the initial size by calling
umpire::Allocator::release()
:
pooled_allocator.release();
The complete example is included below:
//////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2016-20, Lawrence Livermore National Security, LLC and Umpire
// project contributors. See the COPYRIGHT file for details.
//
// SPDX-License-Identifier: (MIT)
//////////////////////////////////////////////////////////////////////////////
#include "umpire/strategy/DynamicPool.hpp"
#include "umpire/Allocator.hpp"
#include "umpire/ResourceManager.hpp"
#include "umpire/util/Macros.hpp"
#include <iostream>
int main(int, char**) {
auto& rm = umpire::ResourceManager::getInstance();
auto allocator = rm.getAllocator("DEVICE");
/*
* Create a 4 Gb pool and reserve one word (to maintain aligment)
*/
auto pooled_allocator = rm.makeAllocator<umpire::strategy::DynamicPool>(
"GPU_POOL",
allocator,
4ul * 1024ul * 1024ul * 1024ul + 1);
void* hold = pooled_allocator.allocate(64);
UMPIRE_USE_VAR(hold);
std::cout << "Pool has allocated " << pooled_allocator.getActualSize()
<< " bytes of memory. " << pooled_allocator.getCurrentSize()
<< " bytes are used" << std::endl;
/*
* Grow pool to ~12 by grabbing a 8Gb chunk
*/
void* grow = pooled_allocator.allocate( 8ul * 1024ul * 1024ul * 1024ul );
pooled_allocator.deallocate(grow);
std::cout << "Pool has allocated " << pooled_allocator.getActualSize()
<< " bytes of memory. " << pooled_allocator.getCurrentSize()
<< " bytes are used" << std::endl;
/*
* Shrink pool back to ~4Gb
*/
pooled_allocator.release();
std::cout << "Pool has allocated " << pooled_allocator.getActualSize()
<< " bytes of memory. " << pooled_allocator.getCurrentSize()
<< " bytes are used" << std::endl;
return 0;
}