add sampling for guarded objects

include/mimalloc.h

@@ -370,6 +370,7 @@ typedef enum mi_option_e {
   mi_option_guarded_max,                // only used when building with MI_GUARDED: maximal rounded object size for guarded objects (=0)
   mi_option_guarded_precise,            // disregard minimal alignment requirement to always place guarded blocks exactly in front of a guard page (=0)
   mi_option_guarded_sample_rate,        // 1 out of N allocations in the min/max range will be guarded (=1000)
+  mi_option_guarded_sample_seed,        // can be set to allow for a (more) deterministic re-execution when a guard page is triggered (=0)
   _mi_option_last,
   // legacy option names
   mi_option_large_os_pages = mi_option_allow_large_os_pages,

include/mimalloc/internal.h

@@ -91,6 +91,7 @@ void       _mi_tld_init(mi_tld_t* tld, mi_heap_t* bheap);
 mi_threadid_t _mi_thread_id(void) mi_attr_noexcept;
 mi_heap_t*    _mi_heap_main_get(void);     // statically allocated main backing heap
 mi_subproc_t* _mi_subproc_from_id(mi_subproc_id_t subproc_id);
+void       _mi_heap_guarded_init(mi_heap_t* heap);
 
 // os.c
 void       _mi_os_init(void);                                            // called from process init
@@ -610,12 +611,21 @@ static inline bool mi_block_ptr_is_guarded(const mi_block_t* block, const void*
 }
 
 static inline bool mi_heap_malloc_use_guarded(mi_heap_t* heap, size_t size) {
-  MI_UNUSED(heap);
-  return (size <= (size_t)_mi_option_get_fast(mi_option_guarded_max)
-           && size >= (size_t)_mi_option_get_fast(mi_option_guarded_min));
+  MI_UNUSED(heap);  
+  if (heap->guarded_sample_rate==0 ||
+      size > heap->guarded_size_max ||
+      size < heap->guarded_size_min) {
+    return false;
+  }
+  if (++heap->guarded_sample_count < heap->guarded_sample_rate) {
+    return false;
+  }
+  heap->guarded_sample_count = 0;  // reset
+  return true;
 }
 
 mi_decl_restrict void* _mi_heap_malloc_guarded(mi_heap_t* heap, size_t size, bool zero) mi_attr_noexcept;
+
 #endif
 
 

include/mimalloc/types.h

@@ -502,6 +502,13 @@ struct mi_heap_s {
   mi_heap_t*            next;                                // list of heaps per thread
   bool                  no_reclaim;                          // `true` if this heap should not reclaim abandoned pages
   uint8_t               tag;                                 // custom tag, can be used for separating heaps based on the object types
+  #if MI_GUARDED
+  size_t                guarded_size_min;                    // minimal size for guarded objects
+  size_t                guarded_size_max;                    // maximal size for guarded objects
+  size_t                guarded_sample_rate;                 // sample rate (set to 0 to disable guarded pages)
+  size_t                guarded_sample_seed;                 // starting sample count
+  size_t                guarded_sample_count;                // current sample count (wraps at `sample_rate`)
+  #endif
   mi_page_t*            pages_free_direct[MI_PAGES_DIRECT];  // optimize: array where every entry points a page with possibly free blocks in the corresponding queue for that size.
   mi_page_queue_t       pages[MI_BIN_FULL + 1];              // queue of pages for each size class (or "bin")
 };
@@ -594,6 +601,7 @@ typedef struct mi_stats_s {
   mi_stat_counter_t arena_count;
   mi_stat_counter_t arena_crossover_count;
   mi_stat_counter_t arena_rollback_count;
+  mi_stat_counter_t guarded_alloc_count;
 #if MI_STAT>1
   mi_stat_count_t normal_bins[MI_BIN_HUGE+1];
 #endif