mem: fix real_used stats for realloc

A realloc that shrank an allocation accounted twice for the
fragment overhead. Basically each shrinking realloc would
introduce an error in the real_used mem stats, between 8 bytes
(f_malloc, no debugging, 32 bits) and up to 96 bytes (q_malloc
with debugging, 64 bits).
This bug concerns only the accounting part. It does not cause any
memory leak or any real runtime problem. It was introduced
in commit fb9d6e50 (2005).

diff --git a/mem/f_malloc.c b/mem/f_malloc.c
index 2c05fe6..49c4b7a 100644 (file)
--- a/mem/f_malloc.c
+++ b/mem/f_malloc.c
@@ -491,7 +491,9 @@ void* fm_realloc(struct fm_block* qm, void* p, unsigned long size)
                fm_split_frag(qm, f, size);
 #endif
 #if defined(DBG_F_MALLOC) || defined(MALLOC_STATS)
-               qm->real_used-=(orig_size-f->size-FRAG_OVERHEAD);
+               /* fm_split frag already adds FRAG_OVERHEAD for the newly created
+                  free frag, so here we only need orig_size-f->size for real used */
+               qm->real_used-=(orig_size-f->size);
                qm->used-=(orig_size-f->size);
 #endif
        }else if (f->size<size){

diff --git a/mem/q_malloc.c b/mem/q_malloc.c
index 09cb5c7..04c6dc9 100644 (file)
--- a/mem/q_malloc.c
+++ b/mem/q_malloc.c
@@ -562,8 +562,11 @@ void* qm_realloc(struct qm_block* qm, void* p, unsigned long size)
 #else
                if(split_frag(qm, f, size)!=0){
 #endif
-                       /* update used sizes: freed the spitted frag */
-                       qm->real_used-=(orig_size-f->size-FRAG_OVERHEAD);
+                       /* update used sizes: freed the splited frag */
+                       /* split frag already adds FRAG_OVERHEAD for the newly created
+                          free frag, so here we only need orig_size-f->size for real used
+                        */
+                       qm->real_used-=(orig_size-f->size);
                        qm->used-=(orig_size-f->size);
                }