* Reimplemented realloc() to reuse the previous buffer if possible and useful.

* Cleanup.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34409 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/boot/loader/heap.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright 2003-2007, Axel Dörfler, [email protected]. All rights reserved.
+ * Copyright 2003-2009, Axel Dörfler, [email protected].
  * Distributed under the terms of the MIT License.
  */
 
@@ -23,20 +23,20 @@
 #endif
 
 
-/* This is a very simple malloc()/free() implementation - it only
+/*!	This is a very simple malloc()/free() implementation - it only
- * manages a free list.
+	manages a free list.
- * After heap_init() is called, all free memory is contained in one
+	After heap_init() is called, all free memory is contained in one
- * big chunk, the only entry in the free link list (which is a single
+	big chunk, the only entry in the free link list (which is a single
- * linked list).
+	linked list).
- * When memory is allocated, the smallest free chunk that contains
+	When memory is allocated, the smallest free chunk that contains
- * the requested size is split (or taken as a whole if it can't be
+	the requested size is split (or taken as a whole if it can't be
- * splitted anymore), and it's lower half will be removed from the
+	splitted anymore), and it's lower half will be removed from the
- * free list.
+	free list.
- * The free list is ordered by size, starting with the smallest
+	The free list is ordered by size, starting with the smallest
- * free chunk available. When a chunk is freed, it will be joint
+	free chunk available. When a chunk is freed, it will be joint
- * with its predecessor or successor, if possible.
+	with its predecessor or successor, if possible.
- * To ease list handling, the list anchor itself is a free chunk with
+	To ease list handling, the list anchor itself is a free chunk with
- * size 0 that can't be allocated.
+	size 0 that can't be allocated.
 */
 
 #define DEBUG_ALLOCATIONS
@@ -58,6 +58,9 @@ struct free_chunk {
 };
 
 
+const static uint32 kAlignment = 4;
+	// all memory chunks will be a multiple of this
+
 static void* sHeapBase;
 static uint32 /*sHeapSize,*/ sMaxHeapSize, sAvailable;
 static free_chunk sFreeAnchor;
@@ -149,7 +152,8 @@ free_chunk::Remove(free_chunk *previous)
 void
 free_chunk::Enqueue()
 {
-	free_chunk *chunk = sFreeAnchor.next, *last = &sFreeAnchor;
+	free_chunk* chunk = sFreeAnchor.next;
+	free_chunk* last = &sFreeAnchor;
 	while (chunk && chunk->Size() < size) {
 		last = chunk;
 		chunk = chunk->next;
@@ -191,7 +195,8 @@ heap_release(stage2_args *args)
 status_t
 heap_init(stage2_args* args)
 {
-	void *base, *top;
+	void* base;
+	void* top;
 	if (platform_init_heap(args, &base, &top) < B_OK)
 		return B_ERROR;
 
@@ -234,11 +239,13 @@ grow_heap(uint32 bytes)
 void
 dump_chunks(void)
 {
-	free_chunk *chunk = sFreeAnchor.next, *last = &sFreeAnchor;
+	free_chunk* chunk = sFreeAnchor.next;
+	free_chunk* last = &sFreeAnchor;
 	while (chunk != NULL) {
 		last = chunk;
 
-		printf("\t%p: chunk size = %ld, end = %p, next = %p\n", chunk, chunk->size, (uint8 *)chunk + chunk->size, chunk->next);
+		printf("\t%p: chunk size = %ld, end = %p, next = %p\n", chunk,
+			chunk->size, (uint8*)chunk + chunk->size, chunk->next);
 		chunk = chunk->next;
 	}
 }
@@ -257,15 +264,16 @@ malloc(size_t size)
 	if (sHeapBase == NULL || size == 0)
 		return NULL;
 
-	// align the size requirement to a 4 bytes boundary
+	// align the size requirement to a kAlignment bytes boundary
-	size = (size + 3) & 0xfffffffc;
+	size = (size - 1 + kAlignment) & ~(size_t)(kAlignment - 1);
 
 	if (size > sAvailable) {
 		dprintf("malloc(): Out of memory!\n");
 		return NULL;
 	}
 
-	free_chunk *chunk = sFreeAnchor.next, *last = &sFreeAnchor;
+	free_chunk* chunk = sFreeAnchor.next;
+	free_chunk* last = &sFreeAnchor;
 	while (chunk && chunk->Size() < size) {
 		last = chunk;
 		chunk = chunk->next;
@@ -277,10 +285,10 @@ malloc(size_t size)
 		return NULL;
 	}
 
-	if (chunk->Size() > size + sizeof(free_chunk) + 4) {
+	if (chunk->Size() > size + sizeof(free_chunk) + kAlignment) {
 		// if this chunk is bigger than the requested size,
 		// we split it to form two chunks (with a minimal
-		// size of 4 allocatable bytes).
+		// size of kAlignment allocatable bytes).
 
 		free_chunk* freeChunk = chunk->Split(size);
 		last->next = freeChunk;
@@ -304,25 +312,34 @@ malloc(size_t size)
 void*
 realloc(void* oldBuffer, size_t newSize)
 {
-	// ToDo: improve this implementation!
-
 	if (newSize == 0) {
 		TRACE("realloc(%p, %lu) -> NULL\n", oldBuffer, newSize);
 		free(oldBuffer);
 		return NULL;
 	}
 
+	size_t copySize = newSize;
+	if (oldBuffer != NULL) {
+		free_chunk* oldChunk = free_chunk::SetToAllocated(oldBuffer);
+
+		// Check if the old buffer still fits, and if it makes sense to keep it
+		if (oldChunk->size >= newSize
+			&& (oldChunk->size < 128 || newSize > oldChunk->size / 3)) {
+			TRACE("realloc(%p, %lu) old buffer is large enough\n",
+				oldBuffer, newSize);
+			return oldChunk->AllocatedAddress();
+		}
+
+		if (copySize > oldChunk->size)
+			copySize = oldChunk->size;
+	}
+
 	void* newBuffer = malloc(newSize);
 	if (newBuffer == NULL)
 		return NULL;
 
-	if (oldBuffer) {
+	if (oldBuffer != NULL) {
-		free_chunk *oldChunk = free_chunk::SetToAllocated(oldBuffer);
+		memcpy(newBuffer, oldBuffer, copySize);
-
-		if (newSize > oldChunk->size)
-			newSize = oldChunk->size;
-
-		memcpy(newBuffer, oldBuffer, newSize);
 		free(oldBuffer);
 	}
 
@@ -359,7 +376,8 @@ free(void *allocated)
 	// try to join the new free chunk with an existing one
 	// it may be joined with up to two chunks
 
-	free_chunk *chunk = sFreeAnchor.next, *last = &sFreeAnchor;
+	free_chunk* chunk = sFreeAnchor.next;
+	free_chunk* last = &sFreeAnchor;
 	int32 joinCount = 0;
 
 	while (chunk) {