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-rw-r--r--libc/stdlib/malloc/malloc.h35
1 files changed, 30 insertions, 5 deletions
diff --git a/libc/stdlib/malloc/malloc.h b/libc/stdlib/malloc/malloc.h
index 187477a67..0cab1dba2 100644
--- a/libc/stdlib/malloc/malloc.h
+++ b/libc/stdlib/malloc/malloc.h
@@ -23,11 +23,26 @@
satisfy a particularly big request). */
#define MALLOC_HEAP_EXTEND_SIZE MALLOC_PAGE_SIZE
-/* The threshold above which blocks are allocated/freed with mmap/munmap,
- rather than using the heap. */
-#define MALLOC_MMAP_THRESHOLD (8*MALLOC_PAGE_SIZE)
+/* When a heap free-area grows above this size, try to unmap it, releasing
+ the memory back to the system. */
+#define MALLOC_UNMAP_THRESHOLD (8*MALLOC_PAGE_SIZE)
+/* When unmapping a free-area, retain this many bytes if it's the only one,
+ to avoid completely emptying the heap. This is only a heuristic -- the
+ existance of another free area, even if it's smaller than
+ MALLOC_MIN_SIZE, will cause us not to reserve anything. */
+#define MALLOC_MIN_SIZE (2*MALLOC_PAGE_SIZE)
+/* For systems with an MMU, use sbrk to map/unmap memory for the malloc
+ heap, instead of mmap/munmap. This is a tradeoff -- sbrk is faster than
+ mmap/munmap, and guarantees contiguous allocation, but is also less
+ flexible, and causes the heap to only be shrinkable from the end. */
+#ifdef __UCLIBC_HAS_MMU__
+#define MALLOC_USE_SBRK
+#endif
+
+
+/* Change this to `#if 1' to cause malloc to emit debugging info to stderr. */
#if 0
#include <stdio.h>
#define MALLOC_DEBUG(fmt, args...) fprintf (stderr, fmt , ##args)
@@ -36,10 +51,20 @@
#endif
+/* Return SZ rounded down to POWER_OF_2_SIZE (which must be power of 2). */
+#define MALLOC_ROUND_DOWN(sz, power_of_2_size) \
+ ((sz) & ~(power_of_2_size - 1))
+/* Return SZ rounded to POWER_OF_2_SIZE (which must be power of 2). */
+#define MALLOC_ROUND_UP(sz, power_of_2_size) \
+ MALLOC_ROUND_DOWN ((sz) + (power_of_2_size - 1), (power_of_2_size))
+
+/* Return SZ rounded down to a multiple MALLOC_PAGE_SIZE. */
+#define MALLOC_ROUND_DOWN_TO_PAGE_SIZE(sz) \
+ MALLOC_ROUND_DOWN (sz, MALLOC_PAGE_SIZE)
/* Return SZ rounded up to a multiple MALLOC_PAGE_SIZE. */
#define MALLOC_ROUND_UP_TO_PAGE_SIZE(sz) \
- (((sz) + (MALLOC_PAGE_SIZE - 1)) & ~(MALLOC_PAGE_SIZE - 1))
+ MALLOC_ROUND_UP (sz, MALLOC_PAGE_SIZE)
-/* The heap used for small allocations. */
+/* The malloc heap. */
extern struct heap __malloc_heap;