don't calloc unnecessairily

Author: danielsn

include/mimalloc/profile.h

@@ -29,8 +29,8 @@ typedef struct mi_heap_s    mi_heap_t;
 // `user_data`     — flexible array member for caller-owned metadata
 //                   (e.g. a captured stack trace).  The number of bytes
 //                   available is _mi_profiler.record_extra_bytes, set at
-//                   mi_profiler_enable() time.  The profiler zeroes this
-//                   region when the record is allocated and never reads it.
+//                   mi_profiler_enable() time.  The profiler does not
+//                   initialize this region and never reads it.
 // ------------------------------------------------------------------
 typedef struct mi_alloc_record_s {
   void*                     ptr;

src/profile.c

@@ -77,8 +77,8 @@ void mi_profiler_enable(size_t initial_threshold, size_t record_extra_bytes,
 // Record memory management
 //
 // Each record is sizeof(mi_alloc_record_t) + record_extra_bytes bytes.
-// The extra bytes are zeroed by _mi_heap_malloc_zero and available to
-// the callback via record->user_data[].
+// The extra bytes are available to the callback via record->user_data[]
+// but are not initialized; the callback must set any fields it will read.
 //
 // Records are allocated from the same mimalloc heap as the sampled
 // object by calling _mi_heap_malloc_zero from inside the allocator.