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sortix--sortix/libmaxsi/heap.cpp

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/******************************************************************************
COPYRIGHT(C) JONAS 'SORTIE' TERMANSEN 2011.
This file is part of LibMaxsi.
LibMaxsi is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option)
any later version.
LibMaxsi is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
more details.
You should have received a copy of the GNU Lesser General Public License
along with LibMaxsi. If not, see <http://www.gnu.org/licenses/>.
heap.cpp
Functions that allocate/free memory from a dynamic memory heap.
******************************************************************************/
#include <libmaxsi/platform.h>
#include <libmaxsi/memory.h>
#include <libmaxsi/error.h>
#ifdef SORTIX_KERNEL
#define HEAP_GROWS_DOWNWARDS
#endif
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#ifndef SORTIX_KERNEL
#include <unistd.h>
#endif
#define PARANOIA 1
#ifdef SORTIX_KERNEL
#include <sortix/platform.h>
#include <sortix/log.h> // DEBUG
#include <sortix/memorymanagement.h>
#include <sortix/panic.h>
#endif
namespace Maxsi
{
namespace Memory
{
//
// This first section is just magic compiler/platform stuff, you should
// skip ahead to the actual algorithm.
//
#ifdef PLATFORM_X64
const size_t MAGIC = 0xDEADDEADDEADDEADUL;
const size_t ALIGNMENT = 16UL;
#else
const size_t MAGIC = 0xDEADDEADUL;
const size_t ALIGNMENT = 8UL;
#endif
const size_t PAGESIZE = 4UL * 1024UL; // 4 KiB
const size_t NUMBINS = 8UL * sizeof(size_t);
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extern addr_t wilderness;
#ifdef SORTIX_KERNEL
addr_t GetHeapStart()
{
return Sortix::Memory::GetHeapUpper();
}
size_t GetHeapMaxSize()
{
return Sortix::Memory::GetHeapUpper() - Sortix::Memory::GetHeapLower();
}
void FreeMemory(addr_t where, size_t bytes)
{
ASSERT( (bytes & (PAGESIZE-1UL)) == 0 );
while ( bytes )
{
addr_t page = Sortix::Memory::UnmapKernel(where);
Sortix::Page::Put(page);
bytes -= PAGESIZE;
where += PAGESIZE;
}
}
bool AllocateMemory(addr_t where, size_t bytes)
{
ASSERT( (bytes & (PAGESIZE-1UL)) == 0 );
addr_t pos = where;
while ( bytes )
{
addr_t page = Sortix::Page::Get();
if ( !page )
{
FreeMemory(where, pos-where);
return false;
}
if ( !Sortix::Memory::MapKernel(page, pos) )
{
Sortix::Page::Put(page);
FreeMemory(where, pos-where);
return false;
}
bytes -= PAGESIZE;
pos += PAGESIZE;
}
return true;
}
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bool ExtendHeap(size_t bytesneeded)
{
#ifdef HEAP_GROWS_DOWNWARDS
addr_t newwilderness = wilderness - bytesneeded;
#else
addr_t newwilderness = wilderness + bytesneeded;
#endif
return AllocateMemory(newwilderness, bytesneeded);
}
#else
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addr_t GetHeapStart()
{
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addr_t base = (addr_t) sbrk(0);
addr_t unaligned = base % ALIGNMENT;
if ( unaligned )
{
sbrk(ALIGNMENT-unaligned);
}
addr_t result = (addr_t) sbrk(0);
return result;
}
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size_t GetHeapMaxSize()
{
// TODO: A bit of a hack!
return SIZE_MAX;
}
bool ExtendHeap(size_t bytesneeded)
{
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void* newheapend = sbrk(bytesneeded);
return newheapend != (void*) -1UL;
}
#endif
// TODO: BitScanForward and BitScanReverse are x86 instructions, but
// directly using them messes with the optimizer. Once possible, use
// the inline assembly instead of the C-version of the functions.
// Returns the index of the most significant set bit.
inline size_t BSR(size_t Value)
{
#if 1
ASSERT(Value > 0);
for ( size_t I = 8*sizeof(size_t); I > 0; I-- )
{
if ( Value & ( 1UL << (I-1) ) ) { return I-1; }
}
return 0;
#else
size_t Result;
asm("bsr %0, %1" : "=r"(Result) : "r"(Value));
return Result;
#endif
}
// Returns the index of the least significant set bit.
inline size_t BSF(size_t Value)
{
#if 1
ASSERT(Value > 0);
for ( size_t I = 0; I < 8*sizeof(size_t); I++ )
{
if ( Value & ( 1UL << I ) ) { return I; }
}
return 0;
#else
size_t Result;
asm("bsf %0, %1" : "=r"(Result) : "r"(Value));
return Result;
#endif
}
//
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// Now for some helper functions and structures.
//
struct Chunk;
struct Trailer;
// The location where the heap originally grows from.
addr_t heapstart;
// If heap grows down: Location of the first mapped page.
// If heap grows up: Location of the first not-mapped page.
addr_t wilderness;
// How many bytes remain in the wilderness.
size_t wildernesssize;
// How many bytes are the heap allow to grow to (including wilderness).
size_t heapmaxsize;
// How many bytes are currently used for chunks in the heap, which
// excludes the wilderness.
size_t heapsize;
// bins[N] contain a linked list of chunks that are at least 2^(N+1)
// bytes, but less than 2^(N+2) bytes. By selecting the proper bin in
// constant time, we can allocate chunks in constant time.
Chunk* bins[NUMBINS];
// Bit N is set if bin[N] contains a chunk.
size_t bincontainschunks;
// A preamble to every chunk providing meta-information.
struct Chunk
{
public:
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size_t size; // Includes size of Chunk and Trailer
union
{
size_t magic;
Chunk* nextunused;
};
public:
bool IsUsed() { return magic == MAGIC; }
Trailer* GetTrailer();
Chunk* LeftNeighbor();
Chunk* RightNeighbor();
bool IsSane();
};
// A trailer ro every chunk providing meta-information.
struct Trailer
{
public:
union
{
size_t magic;
Chunk* prevunused;
};
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size_t size; // Includes size of Chunk and Trailer
public:
bool IsUsed() { return magic == MAGIC; }
Chunk* GetChunk();
};
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const size_t OVERHEAD = sizeof(Chunk) + sizeof(Trailer);
// This is how a real chunk actually looks:
//struct RealChunk
//{
// Chunk header;
// byte data[...];
// Trailer footer;
// };
Trailer* Chunk::GetTrailer()
{
return (Trailer*) (((addr_t) this) + size - sizeof(Trailer));
}
Chunk* Chunk::LeftNeighbor()
{
Trailer* trailer = (Trailer*) (((addr_t) this) - sizeof(Trailer));
return trailer->GetChunk();
}
Chunk* Chunk::RightNeighbor()
{
return (Chunk*) (((addr_t) this) + size);
}
Chunk* Trailer::GetChunk()
{
return (Chunk*) (((addr_t) this) + sizeof(Trailer) - size);
}
bool Chunk::IsSane()
{
if ( !size ) { return false; }
size_t binindex = BSR(size);
Trailer* trailer = GetTrailer();
if ( trailer->size != size ) { return false; }
if ( IsUsed() )
{
if ( bins[binindex] == this ) { return false; }
if ( magic != MAGIC || trailer->magic != magic ) { return false; }
}
if ( !IsUsed() )
{
if ( ((addr_t) nextunused) & (ALIGNMENT-1UL) ) { return false; }
if ( ((addr_t) trailer->prevunused) & (ALIGNMENT-1UL) ) { return false; }
if ( nextunused && nextunused->GetTrailer()->prevunused != this ) { return false; }
if ( trailer->prevunused )
{
if ( bins[binindex] == this ) { return false; }
if ( trailer->prevunused->nextunused != this ) { return false; }
}
if ( !trailer->prevunused )
{
if ( bins[binindex] != this ) { return false; }
if ( !(bincontainschunks & (1UL << binindex)) ) { return false; }
}
}
return true;
}
void InsertChunk(Chunk* chunk)
{
// Insert the chunk into the right bin.
size_t binindex = BSR(chunk->size);
chunk->GetTrailer()->prevunused = NULL;
chunk->nextunused = bins[binindex];
if ( chunk->nextunused )
{
ASSERT(chunk->nextunused->IsSane());
chunk->nextunused->GetTrailer()->prevunused = chunk;
}
bins[binindex] = chunk;
bincontainschunks |= (1UL << binindex);
ASSERT(chunk->IsSane());
}
bool ValidateHeap()
{
bool foundbin[NUMBINS];
for ( size_t i = 0; i < NUMBINS; i++ ) { foundbin[i] = false; }
#ifdef HEAP_GROWS_DOWNWARDS
Chunk* chunk = (Chunk*) (wilderness + wildernesssize);
while ( (addr_t) chunk < heapstart )
#else
Chunk* chunk = (Chunk*) heapstart;
while ( (addr_t) chunk < wilderness - wildernesssize )
#endif
{
size_t timesfound = 0;
for ( size_t i = 0; i < NUMBINS; i++ )
{
if ( chunk == bins[i] ) { foundbin[i] = true; timesfound++; }
}
if ( 1 < timesfound ) { return false; }
if ( !chunk->IsSane() ) { return false; }
chunk = chunk->RightNeighbor();
}
for ( size_t i = 0; i < NUMBINS; i++ )
{
if ( !bins[i] )
{
if ( foundbin[i] ) { return false; }
continue;
}
if ( !foundbin[i] ) { return false; }
if ( !bins[i]->IsSane() ) { return false; }
}
return true;
}
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//
// This is where the actual memory allocation algorithm starts.
//
void Init()
{
heapstart = GetHeapStart();
heapmaxsize = GetHeapMaxSize();
heapsize = 0;
wilderness = heapstart;
wildernesssize = 0;
for ( size_t i = 0; i < NUMBINS; i++ ) { bins[i] = NULL; }
bincontainschunks = 0;
}
// Attempts to expand the wilderness such that it contains at least
// bytesneeded bytes. This is done by mapping new pages onto into the
// virtual address-space.
bool ExpandWilderness(size_t bytesneeded)
{
if ( bytesneeded <= wildernesssize ) { return true; }
bytesneeded -= wildernesssize;
// Align the increase on page boundaries.
const size_t PAGEMASK = ~(PAGESIZE - 1UL);
bytesneeded = ( bytesneeded + PAGESIZE - 1UL ) & PAGEMASK;
ASSERT(bytesneeded >= PAGESIZE);
// TODO: Overflow MAY happen here!
if ( heapmaxsize <= heapsize + wildernesssize + bytesneeded )
{
Error::Set(ENOMEM);
return true;
}
#ifdef HEAP_GROWS_DOWNWARDS
addr_t newwilderness = wilderness - bytesneeded;
#else
addr_t newwilderness = wilderness + bytesneeded;
#endif
// Attempt to map pages so our wilderness grows.
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if ( !ExtendHeap(bytesneeded) ) { return false; }
wildernesssize += bytesneeded;
wilderness = newwilderness;
return true;
}
DUAL_FUNCTION(void*, malloc, Allocate, (size_t size))
{
#if 2 <= PARANOIA
ASSERT(ValidateHeap());
#endif
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// The size field keeps both the allocation and meta information.
size += OVERHEAD;
// Round up to nearest alignment.
size = (size + ALIGNMENT - 1UL) & (~(ALIGNMENT-1UL));
// Find the index of the smallest usable bin.
size_t minbinindex = BSR(size-1UL)+1UL;
// Make a bitmask that filter away all bins that are too small.
size_t minbinmask = ~((1UL << minbinindex) - 1UL);
// Figure out which bins are usable for our chunk.
size_t availablebins = bincontainschunks & minbinmask;
if ( availablebins )
{
// Find the smallest available bin.
size_t binindex = BSF(availablebins);
Chunk* chunk = bins[binindex];
ASSERT(chunk->IsSane());
bins[binindex] = chunk->nextunused;
size_t binsize = 1UL << binindex;
// Mark the bin as empty if we emptied it.
if ( !bins[binindex] )
{
bincontainschunks ^= binsize;
}
else
{
Trailer* trailer = bins[binindex]->GetTrailer();
trailer->prevunused = NULL;
}
ASSERT(!bins[binindex] || bins[binindex]->IsSane());
// If we don't use the entire chunk.
if ( OVERHEAD <= binsize - size )
{
size_t left = binsize - size;
chunk->size -= left;
chunk->GetTrailer()->size = chunk->size;
size_t leftbinindex = BSR(left);
Chunk* leftchunk = chunk->RightNeighbor();
leftchunk->size = left;
Trailer* lefttrailer = leftchunk->GetTrailer();
lefttrailer->size = left;
InsertChunk(leftchunk);
}
chunk->magic = MAGIC;
chunk->GetTrailer()->magic = MAGIC;
#if 2 <= PARANOIA
ASSERT(ValidateHeap());
#endif
addr_t result = ((addr_t) chunk) + sizeof(Chunk);
return (void*) result;
}
// If no bins are available, try to allocate from the wilderness.
// Check if the wilderness can meet our requirements.
if ( wildernesssize < size && !ExpandWilderness(size) )
{
Error::Set(ENOMEM);
return NULL;
}
// Carve a new chunk out of the wilderness and initialize it.
#ifdef HEAP_GROWS_DOWNWARDS
Chunk* chunk = (Chunk*) (wilderness + wildernesssize - size);
#else
Chunk* chunk = (Chunk*) (wilderness - wildernesssize);
#endif
wildernesssize -= size;
heapsize += size;
chunk->size = size;
Trailer* trailer = chunk->GetTrailer();
trailer->size = size;
chunk->magic = MAGIC;
trailer->magic = MAGIC;
#if 2 <= PARANOIA
ASSERT(ValidateHeap());
#endif
addr_t result = ((addr_t) chunk) + sizeof(Chunk);
return (void*) result;
}
bool IsLeftmostChunk(Chunk* chunk)
{
#ifdef HEAP_GROWS_DOWNWARDS
return (addr_t) chunk <= wilderness + wildernesssize;
#else
return heapstart <= (addr_t) chunk;
#endif
}
bool IsRightmostChunk(Chunk* chunk)
{
#ifdef HEAP_GROWS_DOWNWARDS
return heapstart <= (addr_t) chunk + chunk->size;
#else
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return heapstart + heapsize <= (addr_t) chunk + chunk->size;
#endif
}
// Removes a chunk from its bin.
void UnlinkChunk(Chunk* chunk)
{
ASSERT(chunk->IsSane());
Trailer* trailer = chunk->GetTrailer();
if ( trailer->prevunused )
{
ASSERT(trailer->prevunused->IsSane());
trailer->prevunused->nextunused = chunk->nextunused;
if ( chunk->nextunused )
{
ASSERT(chunk->nextunused->IsSane());
chunk->nextunused->GetTrailer()->prevunused = trailer->prevunused;
}
}
else
{
if ( chunk->nextunused )
{
ASSERT(chunk->nextunused->IsSane());
chunk->nextunused->GetTrailer()->prevunused = NULL;
}
size_t binindex = BSR(chunk->size);
ASSERT(bins[binindex] == chunk);
bins[binindex] = chunk->nextunused;
if ( !bins[binindex] ) { bincontainschunks ^= 1UL << binindex; }
else { ASSERT(bins[binindex]->IsSane()); }
}
}
// Transforms a chunk and its neighbors into a single chunk if possible.
void UnifyNeighbors(Chunk** chunk)
{
if ( !IsLeftmostChunk(*chunk) )
{
Chunk* neighbor = (*chunk)->LeftNeighbor();
if ( !neighbor->IsUsed() )
{
size_t size = neighbor->size;
size_t chunksize = (*chunk)->size;
UnlinkChunk(neighbor);
*chunk = neighbor;
(*chunk)->size = size + chunksize;
(*chunk)->GetTrailer()->size = (*chunk)->size;
}
}
if ( !IsRightmostChunk(*chunk) )
{
Chunk* neighbor = (*chunk)->RightNeighbor();
if ( !neighbor->IsUsed() )
{
UnlinkChunk(neighbor);
(*chunk)->size += neighbor->size;
(*chunk)->GetTrailer()->size = (*chunk)->size;
}
}
}
DUAL_FUNCTION(void, free, Free, (void* addr))
{
#if 2 <= PARANOIA
ASSERT(ValidateHeap());
#endif
if ( !addr) { return; }
Chunk* chunk = (Chunk*) ((addr_t) addr - sizeof(Chunk));
ASSERT(chunk->IsUsed());
ASSERT(chunk->IsSane());
UnifyNeighbors(&chunk);
#ifdef HEAP_GROWS_DOWNWARDS
bool nexttowilderness = IsLeftmostChunk(chunk);
#else
bool nexttowilderness = IsRightmostChunk(chunk);
#endif
// If possible, let the wilderness regain the memory.
if ( nexttowilderness )
{
heapsize -= chunk->size;
wildernesssize += chunk->size;
return;
}
InsertChunk(chunk);
#if 2 <= PARANOIA
ASSERT(ValidateHeap());
#endif
}
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extern "C" void* calloc(size_t nmemb, size_t size)
{
size_t total = nmemb * size;
void* result = Allocate(total);
if ( !result ) { return NULL; }
Memory::Set(result, 0, total);
return result;
}
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// TODO: Implement this function properly.
extern "C" void* realloc(void* ptr, size_t size)
{
if ( !ptr ) { return Allocate(size); }
Chunk* chunk = (Chunk*) ((addr_t) ptr - sizeof(Chunk));
ASSERT(chunk->IsUsed());
ASSERT(chunk->IsSane());
size_t allocsize = chunk->size - OVERHEAD;
if ( size < allocsize ) { return ptr; }
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void* newptr = Allocate(size);
if ( !newptr ) { return NULL; }
Memory::Copy(newptr, ptr, allocsize);
Free(ptr);
return newptr;
}
}
}
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void* operator new(size_t Size) { return Maxsi::Memory::Allocate(Size); }
void* operator new[](size_t Size) { return Maxsi::Memory::Allocate(Size); }
void operator delete (void* Addr) { return Maxsi::Memory::Free(Addr); };
void operator delete[](void* Addr) { return Maxsi::Memory::Free(Addr); };