py, gc: Only zero out the extra bytes at the end of the heap chunk.

dpgeorge · dpgeorge · commit 32bef315be8e · 2014-04-26T22:23:42.000+01:00
This is a small optimisation to zero out only the additional bytes that
the caller did not ask for.
diff --git a/py/gc.c b/py/gc.c
@@ -366,17 +366,17 @@ void *gc_alloc(machine_uint_t n_bytes, bool has_finaliser) {
     // get pointer to first block
     void *ret_ptr = (void*)(gc_pool_start + start_block * WORDS_PER_BLOCK);
 
-    // zero out the newly allocated blocks
+    // zero out the additional bytes of the newly allocated blocks
     // This is needed because the blocks may have previously held pointers
     // to the heap and will not be set to something else if the caller
     // doesn't actually use the entire block.  As such they will continue
     // to point to the heap and may prevent other blocks from being reclaimed.
-    memset(ret_ptr, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK);
+    memset(ret_ptr + n_bytes, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK - n_bytes);
 
 #if MICROPY_ENABLE_FINALISER
     if (has_finaliser) {
-        // clear type pointer in case it is never set (now done above in memset)
-        //((mp_obj_base_t*)ret_ptr)->type = MP_OBJ_NULL;
+        // clear type pointer in case it is never set
+        ((mp_obj_base_t*)ret_ptr)->type = MP_OBJ_NULL;
         // set mp_obj flag only if it has a finaliser
         FTB_SET(start_block);
     }
@@ -534,8 +534,8 @@ void *gc_realloc(void *ptr_in, machine_uint_t n_bytes) {
             ATB_FREE_TO_TAIL(bl);
         }
 
-        // zero out the newly allocated blocks (see comment above in gc_alloc)
-        memset(ptr_in + n_blocks * BYTES_PER_BLOCK, 0, (new_blocks - n_blocks) * BYTES_PER_BLOCK);
+        // zero out the additional bytes of the newly allocated blocks (see comment above in gc_alloc)
+        memset(ptr_in + n_bytes, 0, new_blocks * BYTES_PER_BLOCK - n_bytes);
 
         return ptr_in;
     }
diff --git a/py/malloc.c b/py/malloc.c
@@ -88,13 +88,9 @@ void *m_malloc_with_finaliser(int num_bytes) {
 
 void *m_malloc0(int num_bytes) {
     void *ptr = m_malloc(num_bytes);
-#if MICROPY_ENABLE_GC
-    // the GC already zeros out all memory
-#else
     if (ptr != NULL) {
         memset(ptr, 0, num_bytes);
     }
-#endif
     return ptr;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -88,13 +88,9 @@ void *m_malloc_with_finaliser(int num_bytes) {`
`88`	`88`
`89`	`89`	`void *m_malloc0(int num_bytes) {`
`90`	`90`	`void *ptr = m_malloc(num_bytes);`
`91`		`-#if MICROPY_ENABLE_GC`
`92`		`- // the GC already zeros out all memory`
`93`		`-#else`
`94`	`91`	`if (ptr != NULL) {`
`95`	`92`	`memset(ptr, 0, num_bytes);`
`96`	`93`	`}`
`97`		`-#endif`
`98`	`94`	`return ptr;`
`99`	`95`	`}`
`100`	`96`