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-rw-r--r--libc/stdlib/malloc/heap_free.c53
1 files changed, 24 insertions, 29 deletions
diff --git a/libc/stdlib/malloc/heap_free.c b/libc/stdlib/malloc/heap_free.c
index 272327260..ad8de5182 100644
--- a/libc/stdlib/malloc/heap_free.c
+++ b/libc/stdlib/malloc/heap_free.c
@@ -16,30 +16,34 @@
#include "heap.h"
-/* Return the memory area MEM of size SIZE to HEAP. */
+/* Return the block of memory at MEM, of size SIZE, to HEAP. */
struct heap_free_area *
__heap_free (struct heap *heap, void *mem, size_t size)
{
- struct heap_free_area *prev_fa, *fa;
+ struct heap_free_area *fa, *prev_fa;
void *end = (char *)mem + size;
HEAP_DEBUG (heap, "before __heap_free");
- /* Find an adjacent free-list entry. */
+ /* Find the right position in the free-list entry to place the new block.
+ This is the most speed critical loop in this malloc implementation:
+ since we use a simple linked-list for the free-list, and we keep it in
+ address-sorted order, it can become very expensive to insert something
+ in the free-list when it becomes fragmented and long. [A better
+ implemention would use a balanced tree or something for the free-list,
+ though that bloats the code-size and complexity quite a bit.] */
for (prev_fa = 0, fa = heap->free_areas; fa; prev_fa = fa, fa = fa->next)
+ if (unlikely (HEAP_FREE_AREA_END (fa) >= mem))
+ break;
+
+ if (fa && HEAP_FREE_AREA_START (fa) <= end)
+ /* The free-list FA is adjacent to the new block, merge them. */
{
- size_t fa_size = fa->size;
- void *fa_mem = HEAP_FREE_AREA_START (fa);
+ size_t fa_size = fa->size + size;
- if (fa_mem > end)
- /* We've reached the right spot in the free-list without finding an
- adjacent free-area, so continue below to add a new free area. */
- break;
- else if (fa_mem == end)
- /* FA is just after MEM, grow down to encompass it. */
+ if (HEAP_FREE_AREA_START (fa) == end)
+ /* FA is just after the new block, grow down to encompass it. */
{
- fa_size += size;
-
/* See if FA can now be merged with its predecessor. */
if (prev_fa && mem == HEAP_FREE_AREA_END (prev_fa))
/* Yup; merge PREV_FA's info into FA. */
@@ -47,18 +51,12 @@ __heap_free (struct heap *heap, void *mem, size_t size)
fa_size += prev_fa->size;
__heap_link_free_area_after (heap, fa, prev_fa->prev);
}
-
- fa->size = fa_size;
-
- goto done;
}
- else if (HEAP_FREE_AREA_END (fa) == mem)
- /* FA is just before MEM, expand to encompass it. */
+ else
+ /* FA is just before the new block, expand to encompass it. */
{
struct heap_free_area *next_fa = fa->next;
- fa_size += size;
-
/* See if FA can now be merged with its successor. */
if (next_fa && end == HEAP_FREE_AREA_START (next_fa))
/* Yup; merge FA's info into NEXT_FA. */
@@ -77,17 +75,14 @@ __heap_free (struct heap *heap, void *mem, size_t size)
/* Update links with the neighbors in the list. */
__heap_link_free_area (heap, fa, prev_fa, next_fa);
}
-
- fa->size = fa_size;
-
- goto done;
}
- }
- /* Make MEM into a new free-list entry. */
- fa = __heap_add_free_area (heap, mem, size, prev_fa, fa);
+ fa->size = fa_size;
+ }
+ else
+ /* Make the new block into a separate free-list entry. */
+ fa = __heap_add_free_area (heap, mem, size, prev_fa, fa);
- done:
HEAP_DEBUG (heap, "after __heap_free");
return fa;