Kokkos_MemoryPool.hpp
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Kokkos_MemoryPool.hpp
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			// Kokkos v. 2.0
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			#ifndef KOKKOS_MEMORYPOOL_HPP
			#define KOKKOS_MEMORYPOOL_HPP

			#include <Kokkos_Core_fwd.hpp>
			#include <Kokkos_Parallel.hpp>
			#include <Kokkos_Atomic.hpp>
			#include <impl/Kokkos_BitOps.hpp>
			#include <impl/Kokkos_Error.hpp>
			#include <impl/Kokkos_SharedAlloc.hpp>

			#include <limits>
			#include <algorithm>
			#include <chrono>

			// How should errors be handled? In general, production code should return a
			// value indicating failure so the user can decide how the error is handled.
			// While experimental, code can abort instead. If KOKKOS_ENABLE_MEMPOOL_PRINTERR is
			// defined, the code will abort with an error message. Otherwise, the code will
			// return with a value indicating failure when possible, or do nothing instead.
			//#define KOKKOS_ENABLE_MEMPOOL_PRINTERR

			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_INFO
			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_CONSTRUCTOR_INFO
			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_BLOCKSIZE_INFO
			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_SUPERBLOCK_INFO
			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_ACTIVE_SUPERBLOCKS
			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_PAGE_INFO
			//#define KOKKOS_ENABLE_MEMPOOL_PRINT_INDIVIDUAL_PAGE_INFO

			//----------------------------------------------------------------------------

			namespace Kokkos {
			namespace Experimental {

			namespace MempoolImpl {

			template < typename T, typename ExecutionSpace >
			struct initialize_array {
			typedef ExecutionSpace execution_space;
			typedef typename ExecutionSpace::size_type size_type;

			T * m_data;
			T m_value;

			initialize_array( T * d, size_t size, T v ) : m_data( d ), m_value( v )
			{
			Kokkos::parallel_for( size, *this );

			execution_space::fence();
			}

			KOKKOS_INLINE_FUNCTION
			void operator()( size_type i ) const { m_data[i] = m_value; }
			};

			template <typename Bitset>
			struct bitset_count
			{
			typedef typename Bitset::execution_space execution_space;
			typedef typename execution_space::size_type size_type;
			typedef typename Bitset::size_type value_type;
			typedef typename Bitset::word_type word_type;

			word_type * m_words;
			value_type & m_result;

			bitset_count( word_type * w, value_type num_words, value_type & r )
			: m_words( w ), m_result( r )
			{
			parallel_reduce( num_words, *this, m_result );
			}

			KOKKOS_INLINE_FUNCTION
			void init( value_type & v ) const
			{ v = 0; }

			KOKKOS_INLINE_FUNCTION
			void join( volatile value_type & dst, volatile value_type const & src ) const
			{ dst += src; }

			KOKKOS_INLINE_FUNCTION
			void operator()( size_type i, value_type & count ) const
			{
			count += Kokkos::Impl::bit_count( m_words[i] );
			}
			};

			template < typename Device >
			class Bitset {
			public:
			typedef typename Device::execution_space execution_space;
			typedef typename Device::memory_space memory_space;
			typedef unsigned word_type;
			typedef unsigned size_type;

			typedef Kokkos::Impl::DeepCopy< memory_space, Kokkos::HostSpace > raw_deep_copy;

			// Define some constants.
			enum {
			// Size of bitset word. Should be 32.
			WORD_SIZE = sizeof(word_type) * CHAR_BIT,
			LG_WORD_SIZE = Kokkos::Impl::integral_power_of_two( WORD_SIZE ),
			WORD_MASK = WORD_SIZE - 1
			};

			private:
			word_type * m_words;
			size_type m_size;
			size_type m_num_words;
			word_type m_last_word_mask;

			public:
			~Bitset() = default;
			Bitset() = default;
			Bitset( Bitset && ) = default;
			Bitset( const Bitset & ) = default;
			Bitset & operator = ( Bitset && ) = default;
			Bitset & operator = ( const Bitset & ) = default;

			void init( void * w, size_type s )
			{
			// Assumption: The size of the memory pointed to by w is a multiple of
			// sizeof(word_type).

			m_words = reinterpret_cast<word_type*>( w );
			m_size = s;
			m_num_words = ( s + WORD_SIZE - 1 ) >> LG_WORD_SIZE;
			m_last_word_mask = m_size & WORD_MASK ? ( word_type(1) << ( m_size & WORD_MASK ) ) - 1 : 0;

			reset();
			}

			size_type size() const { return m_size; }

			size_type count() const
			{
			size_type val = 0;
			bitset_count< Bitset > bc( m_words, m_num_words, val );
			return val;
			}

			void set()
			{
			// Set all the bits.
			initialize_array< word_type, execution_space > ia( m_words, m_num_words, ~word_type(0) );

			if ( m_last_word_mask ) {
			// Clear the unused bits in the last block.
			raw_deep_copy( m_words + ( m_num_words - 1 ), &m_last_word_mask, sizeof(word_type) );
			}
			}

			void reset()
			{
			initialize_array< word_type, execution_space > ia( m_words, m_num_words, word_type(0) );
			}

			KOKKOS_FORCEINLINE_FUNCTION
			bool test( size_type i ) const
			{
			size_type word_pos = i >> LG_WORD_SIZE;
			word_type word = volatile_load( &m_words[ word_pos ] );
			word_type mask = word_type(1) << ( i & WORD_MASK );

			return word & mask;
			}

			KOKKOS_FORCEINLINE_FUNCTION
			bool set( size_type i ) const
			{
			size_type word_pos = i >> LG_WORD_SIZE;
			word_type mask = word_type(1) << ( i & WORD_MASK );

			return !( atomic_fetch_or( &m_words[ word_pos ], mask ) & mask );
			}

			KOKKOS_FORCEINLINE_FUNCTION
			bool reset( size_type i ) const
			{
			size_type word_pos = i >> LG_WORD_SIZE;
			word_type mask = word_type(1) << ( i & WORD_MASK );

			return atomic_fetch_and( &m_words[ word_pos ], ~mask ) & mask;
			}

			KOKKOS_FORCEINLINE_FUNCTION
			Kokkos::pair< bool, word_type >
			fetch_word_set( size_type i ) const
			{
			size_type word_pos = i >> LG_WORD_SIZE;
			word_type mask = word_type(1) << ( i & WORD_MASK );

			Kokkos::pair<bool, word_type> result;
			result.second = atomic_fetch_or( &m_words[ word_pos ], mask );
			result.first = !( result.second & mask );

			return result;
			}

			KOKKOS_FORCEINLINE_FUNCTION
			Kokkos::pair< bool, word_type >
			fetch_word_reset( size_type i ) const
			{
			size_type word_pos = i >> LG_WORD_SIZE;
			word_type mask = word_type(1) << ( i & WORD_MASK );

			Kokkos::pair<bool, word_type> result;
			result.second = atomic_fetch_and( &m_words[ word_pos ], ~mask );
			result.first = result.second & mask;

			return result;
			}

			KOKKOS_FORCEINLINE_FUNCTION
			Kokkos::pair< bool, word_type >
			set_any_in_word( size_type & pos ) const
			{
			size_type word_pos = pos >> LG_WORD_SIZE;
			word_type word = volatile_load( &m_words[ word_pos ] );

			// Loop until there are no more unset bits in the word.
			while ( ~word ) {
			// Find the first unset bit in the word.
			size_type bit = Kokkos::Impl::bit_scan_forward( ~word );

			// Try to set the bit.
			word_type mask = word_type(1) << bit;
			word = atomic_fetch_or( &m_words[ word_pos ], mask );

			if ( !( word & mask ) ) {
			// Successfully set the bit.
			pos = ( word_pos << LG_WORD_SIZE ) + bit;

			return Kokkos::pair<bool, word_type>( true, word );
			}
			}

			// Didn't find a free bit in this word.
			return Kokkos::pair<bool, word_type>( false, word_type(0) );
			}

			KOKKOS_FORCEINLINE_FUNCTION
			Kokkos::pair< bool, word_type >
			set_any_in_word( size_type & pos, word_type word_mask ) const
			{
			size_type word_pos = pos >> LG_WORD_SIZE;
			word_type word = volatile_load( &m_words[ word_pos ] );
			word = ( ~word ) & word_mask;

			// Loop until there are no more unset bits in the word.
			while ( word ) {
			// Find the first unset bit in the word.
			size_type bit = Kokkos::Impl::bit_scan_forward( word );

			// Try to set the bit.
			word_type mask = word_type(1) << bit;
			word = atomic_fetch_or( &m_words[ word_pos ], mask );

			if ( !( word & mask ) ) {
			// Successfully set the bit.
			pos = ( word_pos << LG_WORD_SIZE ) + bit;

			return Kokkos::pair<bool, word_type>( true, word );
			}

			word = ( ~word ) & word_mask;
			}

			// Didn't find a free bit in this word.
			return Kokkos::pair<bool, word_type>( false, word_type(0) );
			}

			KOKKOS_FORCEINLINE_FUNCTION
			Kokkos::pair< bool, word_type >
			reset_any_in_word( size_type & pos ) const
			{
			size_type word_pos = pos >> LG_WORD_SIZE;
			word_type word = volatile_load( &m_words[ word_pos ] );

			// Loop until there are no more set bits in the word.
			while ( word ) {
			// Find the first unset bit in the word.
			size_type bit = Kokkos::Impl::bit_scan_forward( word );

			// Try to reset the bit.
			word_type mask = word_type(1) << bit;
			word = atomic_fetch_and( &m_words[ word_pos ], ~mask );

			if ( word & mask ) {
			// Successfully reset the bit.
			pos = ( word_pos << LG_WORD_SIZE ) + bit;

			return Kokkos::pair<bool, word_type>( true, word );
			}
			}

			// Didn't find a free bit in this word.
			return Kokkos::pair<bool, word_type>( false, word_type(0) );
			}

			KOKKOS_FORCEINLINE_FUNCTION
			Kokkos::pair< bool, word_type >
			reset_any_in_word( size_type & pos, word_type word_mask ) const
			{
			size_type word_pos = pos >> LG_WORD_SIZE;
			word_type word = volatile_load( &m_words[ word_pos ] );
			word = word & word_mask;

			// Loop until there are no more set bits in the word.
			while ( word ) {
			// Find the first unset bit in the word.
			size_type bit = Kokkos::Impl::bit_scan_forward( word );

			// Try to reset the bit.
			word_type mask = word_type(1) << bit;
			word = atomic_fetch_and( &m_words[ word_pos ], ~mask );

			if ( word & mask ) {
			// Successfully reset the bit.
			pos = ( word_pos << LG_WORD_SIZE ) + bit;

			return Kokkos::pair<bool, word_type>( true, word );
			}

			word = word & word_mask;
			}

			// Didn't find a free bit in this word.
			return Kokkos::pair<bool, word_type>( false, word_type(0) );
			}
			};

			template < typename UInt32View, typename BSHeaderView, typename SBHeaderView,
			typename MempoolBitset >
			struct create_histogram {
			typedef typename UInt32View::execution_space execution_space;
			typedef typename execution_space::size_type size_type;
			typedef Kokkos::pair< double, uint32_t > value_type;

			size_t m_start;
			UInt32View m_page_histogram;
			BSHeaderView m_blocksize_info;
			SBHeaderView m_sb_header;
			MempoolBitset m_sb_blocks;
			size_t m_lg_max_sb_blocks;
			uint32_t m_lg_min_block_size;
			uint32_t m_blocks_per_page;
			value_type & m_result;

			create_histogram( size_t start, size_t end, UInt32View ph, BSHeaderView bsi,
			SBHeaderView sbh, MempoolBitset sbb, size_t lmsb,
			uint32_t lmbs, uint32_t bpp, value_type & r )
			: m_start( start ), m_page_histogram( ph ), m_blocksize_info( bsi ),
			m_sb_header( sbh ), m_sb_blocks( sbb ), m_lg_max_sb_blocks( lmsb ),
			m_lg_min_block_size( lmbs ), m_blocks_per_page( bpp ), m_result( r )
			{
			Kokkos::parallel_reduce( end - start, *this, m_result );

			execution_space::fence();
			}

			KOKKOS_INLINE_FUNCTION
			void init( value_type & v ) const
			{
			v.first = 0.0;
			v.second = 0;
			}

			KOKKOS_INLINE_FUNCTION
			void join( volatile value_type & dst, volatile value_type const & src ) const
			{
			dst.first += src.first;
			dst.second += src.second;
			}

			KOKKOS_INLINE_FUNCTION
			void operator()( size_type i, value_type & r ) const
			{
			size_type i2 = i + m_start;

			uint32_t lg_block_size = m_sb_header(i2).m_lg_block_size;

			// A superblock only has a block size of 0 when it is empty.
			if ( lg_block_size != 0 ) {
			uint32_t block_size_id = lg_block_size - m_lg_min_block_size;
			uint32_t blocks_per_sb = m_blocksize_info[block_size_id].m_blocks_per_sb;
			uint32_t pages_per_sb = m_blocksize_info[block_size_id].m_pages_per_sb;

			uint32_t total_allocated_blocks = 0;

			for ( uint32_t j = 0; j < pages_per_sb; ++j ) {
			unsigned start_pos = ( i2 << m_lg_max_sb_blocks ) + j * m_blocks_per_page;
			unsigned end_pos = start_pos + m_blocks_per_page;
			uint32_t page_allocated_blocks = 0;

			for ( unsigned k = start_pos; k < end_pos; ++k ) {
			page_allocated_blocks += m_sb_blocks.test( k );
			}

			total_allocated_blocks += page_allocated_blocks;

			atomic_increment( &m_page_histogram(page_allocated_blocks) );
			}

			r.first += double(total_allocated_blocks) / blocks_per_sb;
			r.second += blocks_per_sb;
			}
			}
			};

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_SUPERBLOCK_INFO
			template < typename UInt32View, typename SBHeaderView, typename MempoolBitset >
			struct count_allocated_blocks {
			typedef typename UInt32View::execution_space execution_space;
			typedef typename execution_space::size_type size_type;

			UInt32View m_num_allocated_blocks;
			SBHeaderView m_sb_header;
			MempoolBitset m_sb_blocks;
			size_t m_sb_size;
			size_t m_lg_max_sb_blocks;

			count_allocated_blocks( size_t num_sb, UInt32View nab, SBHeaderView sbh,
			MempoolBitset sbb, size_t sbs, size_t lmsb )
			: m_num_allocated_blocks( nab ), m_sb_header( sbh ),
			m_sb_blocks( sbb ), m_sb_size( sbs ), m_lg_max_sb_blocks( lmsb )
			{
			Kokkos::parallel_for( num_sb, *this );

			execution_space::fence();
			}

			KOKKOS_INLINE_FUNCTION
			void operator()( size_type i ) const
			{
			uint32_t lg_block_size = m_sb_header(i).m_lg_block_size;

			// A superblock only has a block size of 0 when it is empty.
			if ( lg_block_size != 0 ) {
			// Count the allocated blocks in the superblock.
			uint32_t blocks_per_sb = lg_block_size > 0 ? m_sb_size >> lg_block_size : 0;
			unsigned start_pos = i << m_lg_max_sb_blocks;
			unsigned end_pos = start_pos + blocks_per_sb;
			uint32_t count = 0;

			for ( unsigned j = start_pos; j < end_pos; ++j ) {
			count += m_sb_blocks.test( j );
			}

			m_num_allocated_blocks(i) = count;
			}
			}
			};
			#endif

			}

			/// \class MemoryPool
			/// \brief Bitset based memory manager for pools of same-sized chunks of memory.
			/// \tparam Device Kokkos device that gives the execution and memory space the
			/// allocator will be used in.
			///
			/// MemoryPool is a memory space that can be on host or device. It provides a
			/// pool memory allocator for fast allocation of same-sized chunks of memory.
			/// The memory is only accessible on the host / device this allocator is
			/// associated with.
			///
			/// This allocator is based on ideas from the following GPU allocators:
			/// Halloc (https://github.com/canonizer/halloc).
			/// ScatterAlloc (https://github.com/ComputationalRadiationPhysics/scatteralloc)
			template < typename Device >
			class MemoryPool {
			private:
			// The allocator uses superblocks. A superblock is divided into pages, and a
			// page is divided into blocks. A block is the chunk of memory that is given
			// out by the allocator. A page always has a number of blocks equal to the
			// size of the word used by the bitset. Thus, the pagesize can vary between
			// superblocks as it is based on the block size of the superblock. The
			// allocator supports all powers of 2 from MIN_BLOCK_SIZE to the size of a
			// superblock as block sizes.

			// Superblocks are divided into 4 categories:
			// 1. empty - is completely empty; there are no active allocations
			// 2. partfull - partially full; there are some active allocations
			// 3. full - full enough with active allocations that new allocations
			// will likely fail
			// 4. active - is currently the active superblock for a block size
			//
			// An inactive superblock is one that is empty, partfull, or full.
			//
			// New allocations occur only from an active superblock. If a superblock is
			// made inactive after an allocation request is made to it but before the
			// allocation request is fulfilled, the allocation will still be attempted
			// from that superblock. Deallocations can occur to partfull, full, or
			// active superblocks. Superblocks move between categories as allocations
			// and deallocations happen. Superblocks all start empty.
			//
			// Here are the possible moves between categories:
			// empty -> active During allocation, there is no active superblock
			// or the active superblock is full.
			// active -> full During allocation, the full threshold of the
			// superblock is reached when increasing the fill
			// level.
			// full -> partfull During deallocation, the full threshold of the
			// superblock is crossed when decreasing the fill
			// level.
			// partfull -> empty Deallocation of the last allocated block of an
			// inactive superblock.
			// partfull -> active During allocation, the active superblock is full.
			//
			// When a new active superblock is needed, partfull superblocks of the same
			// block size are chosen over empty superblocks.
			//
			// The empty and partfull superblocks are tracked using bitsets that represent
			// the superblocks in those repsective categories. Empty superblocks use a
			// single bitset, while partfull superblocks use a bitset per block size
			// (contained sequentially in a single bitset). Active superblocks are
			// tracked by the active superblocks array. Full superblocks aren't tracked
			// at all.

			typedef typename Device::execution_space execution_space;
			typedef typename Device::memory_space backend_memory_space;
			typedef Device device_type;
			typedef MempoolImpl::Bitset< device_type > MempoolBitset;

			// Define some constants.
			enum {
			MIN_BLOCK_SIZE = 64,
			LG_MIN_BLOCK_SIZE = Kokkos::Impl::integral_power_of_two( MIN_BLOCK_SIZE ),
			MAX_BLOCK_SIZES = 31 - LG_MIN_BLOCK_SIZE + 1,

			// Size of bitset word.
			BLOCKS_PER_PAGE = MempoolBitset::WORD_SIZE,
			LG_BLOCKS_PER_PAGE = MempoolBitset::LG_WORD_SIZE,

			INVALID_SUPERBLOCK = ~uint32_t(0),
			SUPERBLOCK_LOCK = ~uint32_t(0) - 1,

			MAX_TRIES = 32 // Cap on the number of pages searched
			// before an allocation returns empty.
			};

			public:
			// Stores information about each superblock.
			struct SuperblockHeader {
			uint32_t m_full_pages;
			uint32_t m_empty_pages;
			uint32_t m_lg_block_size;
			uint32_t m_is_active;

			KOKKOS_FUNCTION
			SuperblockHeader() :
			m_full_pages(0), m_empty_pages(0), m_lg_block_size(0), m_is_active(false) {}
			};

			// Stores information about each block size.
			struct BlockSizeHeader {
			uint32_t m_blocks_per_sb;
			uint32_t m_pages_per_sb;
			uint32_t m_sb_full_level;
			uint32_t m_page_full_level;

			KOKKOS_FUNCTION
			BlockSizeHeader() :
			m_blocks_per_sb(0), m_pages_per_sb(0), m_sb_full_level(0), m_page_full_level(0) {}
			};

			private:
			typedef Kokkos::Impl::SharedAllocationTracker Tracker;
			typedef View< uint32_t *, device_type > UInt32View;
			typedef View< SuperblockHeader *, device_type > SBHeaderView;

			// The letters 'sb' used in any variable name mean superblock.

			size_t m_lg_sb_size; // Log2 of superblock size.
			size_t m_sb_size; // Superblock size.
			size_t m_lg_max_sb_blocks; // Log2 of the number of blocks of the
			// minimum block size in a superblock.
			size_t m_num_sb; // Number of superblocks.
			size_t m_ceil_num_sb; // Number of superblocks rounded up to the smallest
			// multiple of the bitset word size. Used by
			// bitsets representing superblock categories to
			// ensure different block sizes never share a word
			// in the bitset.
			size_t m_num_block_size; // Number of block sizes supported.
			size_t m_data_size; // Amount of memory available to the allocator.
			size_t m_sb_blocks_size; // Amount of memory for free / empty blocks bitset.
			size_t m_empty_sb_size; // Amount of memory for empty superblocks bitset.
			size_t m_partfull_sb_size; // Amount of memory for partfull superblocks bitset.
			size_t m_total_size; // Total amount of memory allocated.
			char * m_data; // Beginning device memory location used for
			// superblocks.
			UInt32View m_active; // Active superblocks IDs.
			SBHeaderView m_sb_header; // Header info for superblocks.
			MempoolBitset m_sb_blocks; // Bitsets representing free / allocated status
			// of blocks in superblocks.
			MempoolBitset m_empty_sb; // Bitset representing empty superblocks.
			MempoolBitset m_partfull_sb; // Bitsets representing partially full superblocks.
			Tracker m_track; // Tracker for superblock memory.
			BlockSizeHeader m_blocksize_info[MAX_BLOCK_SIZES]; // Header info for block sizes.

			// There were several methods tried for storing the block size header info: in a View,
			// in a View of const data, and in a RandomAccess View. All of these were slower than
			// storing it in a static array that is a member variable to the class. In the latter
			// case, the block size info gets copied into the constant memory on the GPU along with
			// the class when it is copied there for exeucting a parallel loop. Instead of storing
			// the values, computing the values every time they were needed was also tried. This
			// method was slightly slower than storing them in the static array.

			public:
			//! Tag this class as a kokkos memory space
			typedef MemoryPool memory_space;

			~MemoryPool() = default;
			MemoryPool() = default;
			MemoryPool( MemoryPool && ) = default;
			MemoryPool( const MemoryPool & ) = default;
			MemoryPool & operator = ( MemoryPool && ) = default;
			MemoryPool & operator = ( const MemoryPool & ) = default;

			/// \brief Initializes the memory pool.
			/// \param memspace The memory space from which the memory pool will allocate memory.
			/// \param total_size The requested memory amount controlled by the allocator. The
			/// actual amount is rounded up to the smallest multiple of the
			/// superblock size >= the requested size.
			/// \param log2_superblock_size Log2 of the size of superblocks used by the allocator.
			/// In most use cases, the default value should work.
			inline
			MemoryPool( const backend_memory_space & memspace,
			size_t total_size, size_t log2_superblock_size = 20 )
			: m_lg_sb_size( log2_superblock_size ),
			m_sb_size( size_t(1) << m_lg_sb_size ),
			m_lg_max_sb_blocks( m_lg_sb_size - LG_MIN_BLOCK_SIZE ),
			m_num_sb( ( total_size + m_sb_size - 1 ) >> m_lg_sb_size ),
			m_ceil_num_sb( ( ( m_num_sb + BLOCKS_PER_PAGE - 1 ) >> LG_BLOCKS_PER_PAGE ) <<
			LG_BLOCKS_PER_PAGE ),
			m_num_block_size( m_lg_sb_size - LG_MIN_BLOCK_SIZE + 1 ),
			m_data_size( m_num_sb * m_sb_size ),
			m_sb_blocks_size( ( m_num_sb << m_lg_max_sb_blocks ) / CHAR_BIT ),
			m_empty_sb_size( m_ceil_num_sb / CHAR_BIT ),
			m_partfull_sb_size( m_ceil_num_sb * m_num_block_size / CHAR_BIT ),
			m_total_size( m_data_size + m_sb_blocks_size + m_empty_sb_size + m_partfull_sb_size ),
			m_data(0),
			m_active( "Active superblocks" ),
			m_sb_header( "Superblock headers" ),
			m_track()
			{
			// Assumption. The minimum block size must be a power of 2.
			static_assert( Kokkos::Impl::is_integral_power_of_two( MIN_BLOCK_SIZE ), "" );

			// Assumption. Require a superblock be large enough so it takes at least 1
			// whole bitset word to represent it using the minimum blocksize.
			if ( m_sb_size < MIN_BLOCK_SIZE * BLOCKS_PER_PAGE ) {
			printf( "\n MemoryPool::MemoryPool() Superblock size must be >= %u \n",
			MIN_BLOCK_SIZE * BLOCKS_PER_PAGE );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			Kokkos::abort( "" );
			}

			// Assumption. A superblock's size can be at most 2^31. Verify this.
			if ( m_lg_sb_size > 31 ) {
			printf( "\n MemoryPool::MemoryPool() Superblock size must be < %u \n",
			( uint32_t(1) << 31 ) );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			Kokkos::abort( "" );
			}

			// Assumption. The Bitset only uses unsigned for size types which limits
			// the amount of memory the allocator can manage. Verify the memory size
			// is below this limit.
			if ( m_data_size > size_t(MIN_BLOCK_SIZE) * std::numeric_limits<unsigned>::max() ) {
			printf( "\n MemoryPool::MemoryPool() Allocator can only manage %lu bytes of memory; requested %lu \n",
			size_t(MIN_BLOCK_SIZE) * std::numeric_limits<unsigned>::max(), total_size );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			Kokkos::abort( "" );
			}

			// Allocate memory for Views. This is done here instead of at construction
			// so that the runtime checks can be performed before allocating memory.
			resize( m_active, m_num_block_size );
			resize( m_sb_header, m_num_sb );

			// Allocate superblock memory.
			typedef Kokkos::Impl::SharedAllocationRecord< backend_memory_space, void > SharedRecord;
			SharedRecord * rec =
			SharedRecord::allocate( memspace, "mempool", m_total_size );

			m_track.assign_allocated_record_to_uninitialized( rec );
			m_data = reinterpret_cast<char *>( rec->data() );

			// Set and initialize the free / empty block bitset memory.
			m_sb_blocks.init( m_data + m_data_size, m_num_sb << m_lg_max_sb_blocks );

			// Set and initialize the empty superblock block bitset memory.
			m_empty_sb.init( m_data + m_data_size + m_sb_blocks_size, m_num_sb );

			// Start with all superblocks in the empty category.
			m_empty_sb.set();

			// Set and initialize the partfull superblock block bitset memory.
			m_partfull_sb.init( m_data + m_data_size + m_sb_blocks_size + m_empty_sb_size,
			m_ceil_num_sb * m_num_block_size );

			// Initialize all active superblocks to be invalid.
			typename UInt32View::HostMirror host_active = create_mirror_view( m_active );
			for ( size_t i = 0; i < m_num_block_size; ++i ) host_active(i) = INVALID_SUPERBLOCK;
			deep_copy( m_active, host_active );

			// A superblock is considered full when this percentage of its pages are full.
			const double superblock_full_fraction = .8;

			// A page is considered full when this percentage of its blocks are full.
			const double page_full_fraction = .875;

			// Initialize the blocksize info.
			for ( size_t i = 0; i < m_num_block_size; ++i ) {
			uint32_t lg_block_size = i + LG_MIN_BLOCK_SIZE;
			uint32_t blocks_per_sb = m_sb_size >> lg_block_size;
			uint32_t pages_per_sb = ( blocks_per_sb + BLOCKS_PER_PAGE - 1 ) >> LG_BLOCKS_PER_PAGE;

			m_blocksize_info[i].m_blocks_per_sb = blocks_per_sb;
			m_blocksize_info[i].m_pages_per_sb = pages_per_sb;

			// Set the full level for the superblock.
			m_blocksize_info[i].m_sb_full_level =
			static_cast<uint32_t>( pages_per_sb * superblock_full_fraction );

			if ( m_blocksize_info[i].m_sb_full_level == 0 ) {
			m_blocksize_info[i].m_sb_full_level = 1;
			}

			// Set the full level for the page.
			uint32_t blocks_per_page =
			blocks_per_sb < BLOCKS_PER_PAGE ? blocks_per_sb : BLOCKS_PER_PAGE;

			m_blocksize_info[i].m_page_full_level =
			static_cast<uint32_t>( blocks_per_page * page_full_fraction );

			if ( m_blocksize_info[i].m_page_full_level == 0 ) {
			m_blocksize_info[i].m_page_full_level = 1;
			}
			}

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_CONSTRUCTOR_INFO
			printf( "\n" );
			printf( " m_lg_sb_size: %12lu\n", m_lg_sb_size );
			printf( " m_sb_size: %12lu\n", m_sb_size );
			printf( " m_max_sb_blocks: %12lu\n", size_t(1) << m_lg_max_sb_blocks );
			printf( "m_lg_max_sb_blocks: %12lu\n", m_lg_max_sb_blocks );
			printf( " m_num_sb: %12lu\n", m_num_sb );
			printf( " m_ceil_num_sb: %12lu\n", m_ceil_num_sb );
			printf( " m_num_block_size: %12lu\n", m_num_block_size );
			printf( " data bytes: %12lu\n", m_data_size );
			printf( " sb_blocks bytes: %12lu\n", m_sb_blocks_size );
			printf( " empty_sb bytes: %12lu\n", m_empty_sb_size );
			printf( " partfull_sb bytes: %12lu\n", m_partfull_sb_size );
			printf( " total bytes: %12lu\n", m_total_size );
			printf( " m_empty_sb size: %12u\n", m_empty_sb.size() );
			printf( "m_partfull_sb size: %12u\n", m_partfull_sb.size() );
			printf( "\n" );
			fflush( stdout );
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_BLOCKSIZE_INFO
			// Print the blocksize info for all the block sizes.
			printf( "SIZE BLOCKS_PER_SB PAGES_PER_SB SB_FULL_LEVEL PAGE_FULL_LEVEL\n" );
			for ( size_t i = 0; i < m_num_block_size; ++i ) {
			printf( "%4zu %13u %12u %13u %15u\n", i + LG_MIN_BLOCK_SIZE,
			m_blocksize_info[i].m_blocks_per_sb, m_blocksize_info[i].m_pages_per_sb,
			m_blocksize_info[i].m_sb_full_level, m_blocksize_info[i].m_page_full_level );
			}
			printf( "\n" );
			#endif
			}

			/// \brief The actual block size allocated given alloc_size.
			KOKKOS_INLINE_FUNCTION
			size_t allocate_block_size( const size_t alloc_size ) const
			{ return size_t(1) << ( get_block_size_index( alloc_size ) + LG_MIN_BLOCK_SIZE ); }

			/// \brief Allocate a chunk of memory.
			/// \param alloc_size Size of the requested allocated in number of bytes.
			///
			/// The function returns a void pointer to a memory location on success and
			/// NULL on failure.
			KOKKOS_FUNCTION
			void * allocate( size_t alloc_size ) const
			{
			void * p = 0;

			// Only support allocations up to the superblock size. Just return 0
			// (failed allocation) for any size above this.
			if ( alloc_size <= m_sb_size )
			{
			int block_size_id = get_block_size_index( alloc_size );
			uint32_t blocks_per_sb = m_blocksize_info[block_size_id].m_blocks_per_sb;
			uint32_t pages_per_sb = m_blocksize_info[block_size_id].m_pages_per_sb;

			#ifdef KOKKOS_IMPL_CUDA_CLANG_WORKAROUND
			// Without this test it looks like pages_per_sb might come back wrong.
			if ( pages_per_sb == 0 ) return NULL;
			#endif

			unsigned word_size = blocks_per_sb > 32 ? 32 : blocks_per_sb;
			unsigned word_mask = ( uint64_t(1) << word_size ) - 1;

			// Instead of forcing an atomic read to guarantee the updated value,
			// reading the old value is actually beneficial because more threads will
			// attempt allocations on the old active superblock instead of waiting on
			// the new active superblock. This will help hide the latency of
			// switching the active superblock.
			uint32_t sb_id = volatile_load( &m_active(block_size_id) );

			// If the active is locked, keep reading it atomically until the lock is
			// released.
			while ( sb_id == SUPERBLOCK_LOCK ) {
			sb_id = atomic_fetch_or( &m_active(block_size_id), uint32_t(0) );
			}

			load_fence();

			bool allocation_done = false;

			while ( !allocation_done ) {
			bool need_new_sb = false;

			if ( sb_id != INVALID_SUPERBLOCK ) {
			// Use the value from the clock register as the hash value.
			uint64_t hash_val = get_clock_register();

			// Get the starting position for this superblock's bits in the bitset.
			uint32_t pos_base = sb_id << m_lg_max_sb_blocks;

			// Mod the hash value to choose a page in the superblock. The
			// initial block searched is the first block of that page.
			uint32_t pos_rel = uint32_t( hash_val & ( pages_per_sb - 1 ) ) << LG_BLOCKS_PER_PAGE;

			// Get the absolute starting position for this superblock's bits in the bitset.
			uint32_t pos = pos_base + pos_rel;

			// Keep track of the number of pages searched. Pages in the superblock are
			// searched linearly from the starting page. All pages in the superblock are
			// searched until either a location is found, or it is proven empty.
			uint32_t pages_searched = 0;

			bool search_done = false;

			while ( !search_done ) {
			bool success = false;
			unsigned prev_val = 0;

			Kokkos::tie( success, prev_val ) = m_sb_blocks.set_any_in_word( pos, word_mask );

			if ( !success ) {
			if ( ++pages_searched >= pages_per_sb ) {
			// Searched all the pages in this superblock. Look for a new superblock.
			//
			// The previous method tried limiting the number of pages searched, but
			// that caused a huge performance issue in CUDA where the outer loop
			// executed massive numbers of times. Threads weren't able to find a
			// free location when the superblock wasn't full and were able to execute
			// the outer loop many times before the superblock was switched for a new
			// one. Switching to an exhaustive search eliminated this possiblity and
			// didn't slow anything down for the tests.
			need_new_sb = true;
			search_done = true;
			}
			else {
			// Move to the next page making sure the new search position
			// doesn't go past this superblock's bits.
			pos += BLOCKS_PER_PAGE;
			pos = ( pos < pos_base + blocks_per_sb ) ? pos : pos_base;
			}
			}
			else {
			// Reserved a memory location to allocate.
			memory_fence();

			search_done = true;
			allocation_done = true;

			uint32_t lg_block_size = block_size_id + LG_MIN_BLOCK_SIZE;

			p = m_data + ( size_t(sb_id) << m_lg_sb_size ) +
			( ( pos - pos_base ) << lg_block_size );

			uint32_t used_bits = Kokkos::Impl::bit_count( prev_val );

			if ( used_bits == 0 ) {
			// This page was empty. Decrement the number of empty pages for
			// the superblock.
			atomic_decrement( &m_sb_header(sb_id).m_empty_pages );
			}
			else if ( used_bits == m_blocksize_info[block_size_id].m_page_full_level - 1 )
			{
			// This page is full. Increment the number of full pages for
			// the superblock.
			uint32_t full_pages = atomic_fetch_add( &m_sb_header(sb_id).m_full_pages, 1 );

			// This allocation made the superblock full, so a new one needs to be found.
			if ( full_pages == m_blocksize_info[block_size_id].m_sb_full_level - 1 ) {
			need_new_sb = true;
			}
			}
			}
			}
			}
			else {
			// This is the first allocation for this block size. A superblock needs
			// to be set as the active one. If this point is reached any other time,
			// it is an error.
			need_new_sb = true;
			}

			if ( need_new_sb ) {
			uint32_t new_sb_id = find_superblock( block_size_id, sb_id );

			if ( new_sb_id == sb_id ) {
			allocation_done = true;
			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_INFO
			printf( " No superblocks available. \n" );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			#endif
			}
			else {
			sb_id = new_sb_id;
			}
			}
			}
			}
			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_INFO
			else {
			printf( " Requested allocation size (%zu) larger than superblock size (%lu). \n",
			alloc_size, m_sb_size );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			}
			#endif

			return p;
			}

			/// \brief Release allocated memory back to the pool.
			/// \param alloc_ptr Pointer to chunk of memory previously allocated by
			/// the allocator.
			/// \param alloc_size Size of the allocated memory in number of bytes.
			KOKKOS_FUNCTION
			void deallocate( void * alloc_ptr, size_t alloc_size ) const
			{
			char * ap = static_cast<char *>( alloc_ptr );

			// Only deallocate memory controlled by this pool.
			if ( ap >= m_data && ap + alloc_size <= m_data + m_data_size ) {
			// Get the superblock for the address. This can be calculated by math on
			// the address since the superblocks are stored contiguously in one memory
			// chunk.
			uint32_t sb_id = ( ap - m_data ) >> m_lg_sb_size;

			// Get the starting position for this superblock's bits in the bitset.
			uint32_t pos_base = sb_id << m_lg_max_sb_blocks;

			// Get the relative position for this memory location's bit in the bitset.
			uint32_t offset = ( ap - m_data ) - ( size_t(sb_id) << m_lg_sb_size );
			uint32_t lg_block_size = m_sb_header(sb_id).m_lg_block_size;
			uint32_t block_size_id = lg_block_size - LG_MIN_BLOCK_SIZE;
			uint32_t pos_rel = offset >> lg_block_size;

			bool success = false;
			unsigned prev_val = 0;

			memory_fence();

			Kokkos::tie( success, prev_val ) = m_sb_blocks.fetch_word_reset( pos_base + pos_rel );

			// If the memory location was previously deallocated, do nothing.
			if ( success ) {
			uint32_t page_fill_level = Kokkos::Impl::bit_count( prev_val );

			if ( page_fill_level == 1 ) {
			// This page is now empty. Increment the number of empty pages for the
			// superblock.
			uint32_t empty_pages = atomic_fetch_add( &m_sb_header(sb_id).m_empty_pages, 1 );

			if ( !volatile_load( &m_sb_header(sb_id).m_is_active ) &&
			empty_pages == m_blocksize_info[block_size_id].m_pages_per_sb - 1 )
			{
			// This deallocation caused the superblock to be empty. Change the
			// superblock category from partially full to empty.
			unsigned pos = block_size_id * m_ceil_num_sb + sb_id;

			if ( m_partfull_sb.reset( pos ) ) {
			// Reset the empty pages and block size for the superblock.
			volatile_store( &m_sb_header(sb_id).m_empty_pages, uint32_t(0) );
			volatile_store( &m_sb_header(sb_id).m_lg_block_size, uint32_t(0) );

			store_fence();

			m_empty_sb.set( sb_id );
			}
			}
			}
			else if ( page_fill_level == m_blocksize_info[block_size_id].m_page_full_level ) {
			// This page is no longer full. Decrement the number of full pages for
			// the superblock.
			uint32_t full_pages = atomic_fetch_sub( &m_sb_header(sb_id).m_full_pages, 1 );

			if ( !volatile_load( &m_sb_header(sb_id).m_is_active ) &&
			full_pages == m_blocksize_info[block_size_id].m_sb_full_level )
			{
			// This deallocation caused the number of full pages to decrease below
			// the full threshold. Change the superblock category from full to
			// partially full.
			unsigned pos = block_size_id * m_ceil_num_sb + sb_id;
			m_partfull_sb.set( pos );
			}
			}
			}
			}
			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINTERR
			else {
			printf( "\n MemoryPool::deallocate() ADDRESS_OUT_OF_RANGE(0x%llx) \n",
			reinterpret_cast<uint64_t>( alloc_ptr ) );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			}
			#endif
			}

			/// \brief Tests if the memory pool has no more memory available to allocate.
			KOKKOS_INLINE_FUNCTION
			bool is_empty() const
			{
			// The allocator is empty if all superblocks are full. A superblock is
			// full if it has >= 80% of its pages allocated.

			// Look at all the superblocks. If one is not full, then the allocator
			// isn't empty.
			for ( size_t i = 0; i < m_num_sb; ++i ) {
			uint32_t lg_block_size = m_sb_header(i).m_lg_block_size;

			// A superblock only has a block size of 0 when it is empty.
			if ( lg_block_size == 0 ) return false;

			uint32_t block_size_id = lg_block_size - LG_MIN_BLOCK_SIZE;
			uint32_t full_pages = volatile_load( &m_sb_header(i).m_full_pages );

			if ( full_pages < m_blocksize_info[block_size_id].m_sb_full_level ) return false;
			}

			// All the superblocks were full. The allocator is empty.
			return true;
			}

			// The following functions are used for debugging.
			void print_status() const
			{
			printf( "\n" );

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_SUPERBLOCK_INFO
			typename SBHeaderView::HostMirror host_sb_header = create_mirror_view( m_sb_header );
			deep_copy( host_sb_header, m_sb_header );

			UInt32View num_allocated_blocks( "Allocated Blocks", m_num_sb );

			// Count the number of allocated blocks per superblock.
			{
			MempoolImpl::count_allocated_blocks< UInt32View, SBHeaderView, MempoolBitset >
			mch( m_num_sb, num_allocated_blocks, m_sb_header,
			m_sb_blocks, m_sb_size, m_lg_max_sb_blocks );
			}

			typename UInt32View::HostMirror host_num_allocated_blocks =
			create_mirror_view( num_allocated_blocks );
			deep_copy( host_num_allocated_blocks, num_allocated_blocks );

			// Print header info of all superblocks.
			printf( "SB_ID SIZE ACTIVE EMPTY_PAGES FULL_PAGES USED_BLOCKS\n" );
			for ( size_t i = 0; i < m_num_sb; ++i ) {
			printf( "%5zu %4u %6d %11u %10u %10u\n", i,
			host_sb_header(i).m_lg_block_size, host_sb_header(i).m_is_active,
			host_sb_header(i).m_empty_pages, host_sb_header(i).m_full_pages,
			host_num_allocated_blocks(i) );
			}

			printf( "\n" );
			#endif

			UInt32View page_histogram( "Page Histogram", 33 );

			// Get a View version of the blocksize info.
			typedef View< BlockSizeHeader *, device_type > BSHeaderView;
			BSHeaderView blocksize_info( "BlockSize Headers", MAX_BLOCK_SIZES );

			Kokkos::Impl::DeepCopy< backend_memory_space, Kokkos::HostSpace >
			dc( blocksize_info.ptr_on_device(), m_blocksize_info,
			sizeof(BlockSizeHeader) * m_num_block_size );

			Kokkos::pair< double, uint32_t > result = Kokkos::pair< double, uint32_t >( 0.0, 0 );

			// Create the page histogram.
			{
			MempoolImpl::create_histogram< UInt32View, BSHeaderView, SBHeaderView, MempoolBitset >
			mch( 0, m_num_sb, page_histogram, blocksize_info, m_sb_header, m_sb_blocks,
			m_lg_max_sb_blocks, LG_MIN_BLOCK_SIZE, BLOCKS_PER_PAGE, result );
			}

			typename UInt32View::HostMirror host_page_histogram = create_mirror_view( page_histogram );
			deep_copy( host_page_histogram, page_histogram );

			// Find the used and total pages and blocks.
			uint32_t used_pages = 0;
			uint32_t used_blocks = 0;
			for ( uint32_t i = 1; i < 33; ++i ) {
			used_pages += host_page_histogram(i);
			used_blocks += i * host_page_histogram(i);
			}
			uint32_t total_pages = used_pages + host_page_histogram(0);

			unsigned num_empty_sb = m_empty_sb.count();
			unsigned num_non_empty_sb = m_num_sb - num_empty_sb;
			unsigned num_partfull_sb = m_partfull_sb.count();

			uint32_t total_blocks = result.second;
			double ave_sb_full = num_non_empty_sb == 0 ? 0.0 : result.first / num_non_empty_sb;
			double percent_used_sb = double( m_num_sb - num_empty_sb ) / m_num_sb;
			double percent_used_pages = total_pages == 0 ? 0.0 : double(used_pages) / total_pages;
			double percent_used_blocks = total_blocks == 0 ? 0.0 : double(used_blocks) / total_blocks;

			// Count active superblocks.
			typename UInt32View::HostMirror host_active = create_mirror_view( m_active );
			deep_copy( host_active, m_active );

			unsigned num_active_sb = 0;
			for ( size_t i = 0; i < m_num_block_size; ++i ) {
			num_active_sb += host_active(i) != INVALID_SUPERBLOCK;
			}

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_ACTIVE_SUPERBLOCKS
			// Print active superblocks.
			printf( "BS_ID SB_ID\n" );
			for ( size_t i = 0; i < m_num_block_size; ++i ) {
			uint32_t sb_id = host_active(i);

			if ( sb_id == INVALID_SUPERBLOCK ) {
			printf( "%5zu I\n", i );
			}
			else if ( sb_id == SUPERBLOCK_LOCK ) {
			printf( "%5zu L\n", i );
			}
			else {
			printf( "%5zu %7u\n", i, sb_id );
			}
			}
			printf( "\n" );
			fflush( stdout );
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_PAGE_INFO
			// Print the summary page histogram.
			printf( "USED_BLOCKS PAGE_COUNT\n" );
			for ( uint32_t i = 0; i < 33; ++i ) {
			printf( "%10u %10u\n", i, host_page_histogram[i] );
			}
			printf( "\n" );
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_INDIVIDUAL_PAGE_INFO
			// Print the page histogram for a few individual superblocks.
			// const uint32_t num_sb_id = 2;
			// uint32_t sb_id[num_sb_id] = { 0, 10 };
			const uint32_t num_sb_id = 1;
			uint32_t sb_id[num_sb_id] = { 0 };

			for ( uint32_t i = 0; i < num_sb_id; ++i ) {
			deep_copy( page_histogram, 0 );

			{
			MempoolImpl::create_histogram< UInt32View, BSHeaderView, SBHeaderView, MempoolBitset >
			mch( sb_id[i], sb_id[i] + 1, page_histogram, blocksize_info, m_sb_header,
			m_sb_blocks, m_lg_max_sb_blocks, LG_MIN_BLOCK_SIZE, BLOCKS_PER_PAGE, result );
			}

			deep_copy( host_page_histogram, page_histogram );

			printf( "SB_ID USED_BLOCKS PAGE_COUNT\n" );
			for ( uint32_t j = 0; j < 33; ++j ) {
			printf( "%5u %10u %10u\n", sb_id[i], j, host_page_histogram[j] );
			}
			printf( "\n" );
			}

			/*
			// Print the blocks used for each page of a few individual superblocks.
			for ( uint32_t i = 0; i < num_sb_id; ++i ) {
			uint32_t lg_block_size = host_sb_header(sb_id[i]).m_lg_block_size;

			if ( lg_block_size != 0 ) {
			printf( "SB_ID BLOCK ID USED_BLOCKS\n" );

			uint32_t block_size_id = lg_block_size - LG_MIN_BLOCK_SIZE;
			uint32_t pages_per_sb = m_blocksize_info[block_size_id].m_pages_per_sb;

			for ( uint32_t j = 0; j < pages_per_sb; ++j ) {
			unsigned start_pos = ( sb_id[i] << m_lg_max_sb_blocks ) + j * BLOCKS_PER_PAGE;
			unsigned end_pos = start_pos + BLOCKS_PER_PAGE;
			uint32_t num_allocated_blocks = 0;

			for ( unsigned k = start_pos; k < end_pos; ++k ) {
			num_allocated_blocks += m_sb_blocks.test( k );
			}

			printf( "%5u %8u %11u\n", sb_id[i], j, num_allocated_blocks );
			}

			printf( "\n" );
			}
			}
			*/
			#endif

			printf( " Used blocks: %10u / %10u = %10.6lf\n", used_blocks, total_blocks,
			percent_used_blocks );
			printf( " Used pages: %10u / %10u = %10.6lf\n", used_pages, total_pages,
			percent_used_pages );
			printf( " Used SB: %10zu / %10zu = %10.6lf\n", m_num_sb - num_empty_sb, m_num_sb,
			percent_used_sb );
			printf( " Active SB: %10u\n", num_active_sb );
			printf( " Empty SB: %10u\n", num_empty_sb );
			printf( " Partfull SB: %10u\n", num_partfull_sb );
			printf( " Full SB: %10lu\n",
			m_num_sb - num_active_sb - num_empty_sb - num_partfull_sb );
			printf( "Ave. SB Full %%: %10.6lf\n", ave_sb_full );
			printf( "\n" );
			fflush( stdout );

			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			}

			KOKKOS_INLINE_FUNCTION
			size_t get_min_block_size() const { return MIN_BLOCK_SIZE; }

			size_t get_mem_size() const { return m_data_size; }

			private:
			/// \brief Returns the index into the active array for the given size.
			///
			/// Computes log2 of the largest power of two >= the given size
			/// ( ie ceil( log2(size) ) ) shifted by LG_MIN_BLOCK_SIZE.
			KOKKOS_FORCEINLINE_FUNCTION
			int get_block_size_index( const size_t size ) const
			{
			// We know the size fits in a 32 bit unsigned because the size of a
			// superblock is limited to 2^31, so casting to an unsigned is safe.

			// Find the most significant nonzero bit.
			uint32_t first_nonzero_bit =
			Kokkos::Impl::bit_scan_reverse( static_cast<unsigned>( size ) );

			// If size is an integral power of 2, ceil( log2(size) ) is equal to the
			// most significant nonzero bit. Otherwise, you need to add 1. Since the
			// minimum block size is MIN_BLOCK_SIZE, make sure ceil( log2(size) ) is at
			// least LG_MIN_BLOCK_SIZE.
			uint32_t lg2_size = first_nonzero_bit + !Kokkos::Impl::is_integral_power_of_two( size );
			lg2_size = lg2_size > LG_MIN_BLOCK_SIZE ? lg2_size : LG_MIN_BLOCK_SIZE;

			// Return ceil( log2(size) ) shifted so that the value for MIN_BLOCK_SIZE
			// is 0.
			return lg2_size - LG_MIN_BLOCK_SIZE;
			}

			/// \brief Finds a superblock with free space to become a new active superblock.
			///
			/// If this function is called, the current active superblock needs to be replaced
			/// because it is full. Initially, only the thread that sets the active superblock
			/// to full calls this function. Other threads can still allocate from the "full"
			/// active superblock because a full superblock still has locations available. If
			/// a thread tries to allocate from the active superblock when it has no free
			/// locations, then that thread will call this function, too, and spin on a lock
			/// waiting until the active superblock has been replaced.
			KOKKOS_FUNCTION
			uint32_t find_superblock( int block_size_id, uint32_t old_sb ) const
			{
			// Try to grab the lock on the head.
			uint32_t lock_sb =
			Kokkos::atomic_compare_exchange( &m_active(block_size_id), old_sb, SUPERBLOCK_LOCK );

			load_fence();

			// Initialize the new superblock to be the previous one so the previous
			// superblock is returned if a new superblock can't be found.
			uint32_t new_sb = lock_sb;

			if ( lock_sb == old_sb ) {
			// This thread has the lock.

			// 1. Look for a partially filled superblock that is of the right block
			// size.

			size_t max_tries = m_ceil_num_sb >> LG_BLOCKS_PER_PAGE;
			size_t tries = 0;
			bool search_done = false;

			// Set the starting search position to the beginning of this block
			// size's bitset.
			unsigned pos = block_size_id * m_ceil_num_sb;

			while ( !search_done ) {
			bool success = false;
			unsigned prev_val = 0;

			Kokkos::tie( success, prev_val ) = m_partfull_sb.reset_any_in_word( pos );

			if ( !success ) {
			if ( ++tries >= max_tries ) {
			// Exceeded number of words for this block size's bitset.
			search_done = true;
			}
			else {
			pos += BLOCKS_PER_PAGE;
			}
			}
			else {
			// Found a superblock.

			// It is possible that the newly found superblock is the same as the
			// old superblock. In this case putting the old value back in yields
			// correct behavior. This could happen as follows. This thread
			// grabs the lock and transitions the superblock to the full state.
			// Before it searches for a new superblock, other threads perform
			// enough deallocations to transition the superblock to the partially
			// full state. This thread then searches for a partially full
			// superblock and finds the one it removed. There's potential for
			// this to cause a performance issue if the same superblock keeps
			// being removed and added due to the right mix and ordering of
			// allocations and deallocations.
			search_done = true;
			new_sb = pos - block_size_id * m_ceil_num_sb;

			// Set the head status for the superblock.
			volatile_store( &m_sb_header(new_sb).m_is_active, uint32_t(true) );

			// If there was a previous active superblock, mark it as not active.
			// It is now in the full category and as such isn't tracked.
			if ( lock_sb != INVALID_SUPERBLOCK ) {
			volatile_store( &m_sb_header(lock_sb).m_is_active, uint32_t(false) );
			}

			store_fence();
			}
			}

			// 2. Look for an empty superblock.
			if ( new_sb == lock_sb ) {
			tries = 0;
			search_done = false;

			// Set the starting search position to the beginning of this block
			// size's bitset.
			pos = 0;

			while ( !search_done ) {
			bool success = false;
			unsigned prev_val = 0;

			Kokkos::tie( success, prev_val ) = m_empty_sb.reset_any_in_word( pos );

			if ( !success ) {
			if ( ++tries >= max_tries ) {
			// Exceeded number of words for this block size's bitset.
			search_done = true;
			}
			else {
			pos += BLOCKS_PER_PAGE;
			}
			}
			else {
			// Found a superblock.

			// It is possible that the newly found superblock is the same as
			// the old superblock. In this case putting the old value back in
			// yields correct behavior. This could happen as follows. This
			// thread grabs the lock and transitions the superblock to the full
			// state. Before it searches for a new superblock, other threads
			// perform enough deallocations to transition the superblock to the
			// partially full state and then the empty state. This thread then
			// searches for a partially full superblock and none exist. This
			// thread then searches for an empty superblock and finds the one
			// it removed. The likelihood of this happening is so remote that
			// the potential for this to cause a performance issue is
			// infinitesimal.
			search_done = true;
			new_sb = pos;

			// Set the empty pages, block size, and head status for the
			// superblock.
			volatile_store( &m_sb_header(new_sb).m_empty_pages,
			m_blocksize_info[block_size_id].m_pages_per_sb );
			volatile_store( &m_sb_header(new_sb).m_lg_block_size,
			block_size_id + LG_MIN_BLOCK_SIZE );
			volatile_store( &m_sb_header(new_sb).m_is_active, uint32_t(true) );

			// If there was a previous active superblock, mark it as not active.
			// It is now in the full category and as such isn't tracked.
			if ( lock_sb != INVALID_SUPERBLOCK ) {
			volatile_store( &m_sb_header(lock_sb).m_is_active, uint32_t(false) );
			}

			store_fence();
			}
			}
			}

			// Write the new active superblock to release the lock.
			atomic_exchange( &m_active(block_size_id), new_sb );
			}
			else {
			// Either another thread has the lock and is switching the active
			// superblock for this block size or another thread has already changed
			// the active superblock since this thread read its value. Keep
			// atomically reading the active superblock until it isn't locked to get
			// the new active superblock.
			do {
			new_sb = atomic_fetch_or( &m_active(block_size_id), uint32_t(0) );
			} while ( new_sb == SUPERBLOCK_LOCK );

			load_fence();

			// Assertions:
			// 1. An invalid superblock should never be found here.
			// 2. If the new superblock is the same as the previous superblock, the
			// allocator is empty.
			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINTERR
			if ( new_sb == INVALID_SUPERBLOCK ) {
			printf( "\n MemoryPool::find_superblock() FOUND_INACTIVE_SUPERBLOCK \n" );
			#ifdef KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST
			fflush( stdout );
			#endif
			Kokkos::abort( "" );
			}
			#endif
			}

			return new_sb;
			}

			/// Returns 64 bits from a clock register.
			KOKKOS_FORCEINLINE_FUNCTION
			uint64_t get_clock_register(void) const
			{
			#if defined( __CUDA_ARCH__ )
			// Return value of 64-bit hi-res clock register.
			return clock64();
			#elif defined( __i386__ ) \|\| defined( __x86_64 )
			// Return value of 64-bit hi-res clock register.
			unsigned a = 0, d = 0;

			__asm__ volatile( "rdtsc" : "=a" (a), "=d" (d) );

			return ( (uint64_t) a ) \| ( ( (uint64_t) d ) << 32 );
			#elif defined( __powerpc ) \|\| defined( __powerpc__ ) \|\| defined( __powerpc64__ ) \|\| \
			defined( __POWERPC__ ) \|\| defined( __ppc__ ) \|\| defined( __ppc64__ )
			unsigned int cycles = 0;

			asm volatile( "mftb %0" : "=r" (cycles) );

			return (uint64_t) cycles;
			#else
			const uint64_t ticks =
			std::chrono::high_resolution_clock::now().time_since_epoch().count();

			return ticks;
			#endif
			}
			};

			} // namespace Experimental
			} // namespace Kokkos

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINTERR
			#undef KOKKOS_ENABLE_MEMPOOL_PRINTERR
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_INFO
			#undef KOKKOS_ENABLE_MEMPOOL_PRINT_INFO
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_BLOCKSIZE_INFO
			#undef KOKKOS_ENABLE_MEMPOOL_PRINT_BLOCKSIZE_INFO
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_SUPERBLOCK_INFO
			#undef KOKKOS_ENABLE_MEMPOOL_PRINT_SUPERBLOCK_INFO
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_PAGE_INFO
			#undef KOKKOS_ENABLE_MEMPOOL_PRINT_PAGE_INFO
			#endif

			#ifdef KOKKOS_ENABLE_MEMPOOL_PRINT_INDIVIDUAL_PAGE_INFO
			#undef KOKKOS_ENABLE_MEMPOOL_PRINT_INDIVIDUAL_PAGE_INFO
			#endif

			#endif // KOKKOS_MEMORYPOOL_HPP

lammps/lib/kokkos/core/src/Kokkos_MemoryPool.hpp383da816c221master

Kokkos_MemoryPool.hppView Options

lammps/lib/kokkos/core/src/Kokkos_MemoryPool.hpp
383da816c221master

Kokkos_MemoryPool.hpp
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