fix bug in bitmap_forall_ranges

src/arena.c

@@ -43,6 +43,7 @@ typedef struct mi_arena_s {
   bool                is_exclusive;         // only allow allocations if specifically for this arena
   bool                is_large;             // memory area consists of large- or huge OS pages (always committed)
   _Atomic(mi_msecs_t) purge_expire;         // expiration time when slices can be purged from `slices_purge`.
+  _Atomic(mi_msecs_t) purge_expire_extend;  // the purge expiration may be extended by a bit
 
   mi_bitmap_t*        slices_free;          // is the slice free?
   mi_bitmap_t*        slices_committed;     // is the slice committed? (i.e. accessible)
@@ -950,7 +951,7 @@ static void mi_arena_free(void* p, size_t size, mi_memid_t memid) {
     mi_assert_internal(mi_memid_needs_no_free(memid));
   }
 
-  // purge expired decommits
+  // try to purge expired decommits
   mi_arenas_try_purge(false, false);
 }
 
@@ -1118,6 +1119,7 @@ static bool mi_manage_os_memory_ex2(void* start, size_t size, bool is_large, int
   arena->numa_node    = numa_node; // TODO: or get the current numa node if -1? (now it allows anyone to allocate on -1)
   arena->is_large     = is_large;
   arena->purge_expire = 0;
+  arena->purge_expire_extend = 0;
   // mi_lock_init(&arena->abandoned_visit_lock);
 
   // init bitmaps
@@ -1402,7 +1404,7 @@ static void mi_arena_purge(mi_arena_t* arena, size_t slice_index, size_t slice_c
     needs_recommit = _mi_os_purge(p, size);
   }
   else {
-    mi_assert_internal(false); // ?
+    mi_assert_internal(false); // can this happen?
   }
 
   // update committed bitmap
@@ -1428,10 +1430,11 @@ static void mi_arena_schedule_purge(mi_arena_t* arena, size_t slice_index, size_
     mi_msecs_t expire = mi_atomic_loadi64_relaxed(&arena->purge_expire);
     if (expire == 0) {
       mi_atomic_storei64_release(&arena->purge_expire, _mi_clock_now() + delay);
+      mi_atomic_storei64_release(&arena->purge_expire_extend, 0);      
+    }
+    else if (mi_atomic_loadi64_acquire(&arena->purge_expire_extend) < 10*delay) {     // limit max extension time
+      mi_atomic_addi64_acq_rel(&arena->purge_expire_extend, (mi_msecs_t)(delay/10));  // add smallish extra delay
     }
-    //else {
-    //  mi_atomic_addi64_acq_rel(&arena->purge_expire, (mi_msecs_t)(delay/10));  // add smallish extra delay
-    //}
     mi_bitmap_setN(arena->slices_purge, slice_index, slice_count, NULL);
   }
 }
@@ -1478,26 +1481,31 @@ static bool mi_arena_try_purge(mi_arena_t* arena, mi_msecs_t now, bool force)
 {
   // check pre-conditions
   if (arena->memid.is_pinned) return false;
-  mi_msecs_t expire = mi_atomic_loadi64_relaxed(&arena->purge_expire);
+  mi_msecs_t expire_base = mi_atomic_loadi64_relaxed(&arena->purge_expire);
+  mi_msecs_t expire_extend = mi_atomic_loadi64_relaxed(&arena->purge_expire_extend);
+  const mi_msecs_t expire = expire_base + expire_extend;
   if (expire == 0) return false;
 
   // expired yet?
   if (!force && expire > now) return false;
 
   // reset expire (if not already set concurrently)
-  mi_atomic_casi64_strong_acq_rel(&arena->purge_expire, &expire, (mi_msecs_t)0);
+  if (mi_atomic_casi64_strong_acq_rel(&arena->purge_expire, &expire_base, (mi_msecs_t)0)) {
+    mi_atomic_storei64_release(&arena->purge_expire_extend, (mi_msecs_t)0); // and also reset the extend
+  }
   _mi_stat_counter_increase(&_mi_stats_main.arena_purges, 1);
 
-  // go through all purge info's
+  // go through all purge info's  (with max MI_BFIELD_BITS ranges at a time)
-  // todo: instead of visiting per-bit, we should visit per range of bits
   mi_purge_visit_info_t vinfo = { now, mi_arena_purge_delay(), true /*all?*/, false /*any?*/};
-  _mi_bitmap_forall_set(arena->slices_purge, &mi_arena_try_purge_visitor, arena, &vinfo);
+  _mi_bitmap_forall_set_ranges(arena->slices_purge, &mi_arena_try_purge_visitor, arena, &vinfo);
 
   // if not fully purged, make sure to purge again in the future
   if (!vinfo.all_purged) {
     const long delay = mi_arena_purge_delay();
     mi_msecs_t expected = 0;
-    mi_atomic_casi64_strong_acq_rel(&arena->purge_expire, &expected, _mi_clock_now() + delay);
+    if (mi_atomic_casi64_strong_acq_rel(&arena->purge_expire, &expected, _mi_clock_now() + delay)) {
+      mi_atomic_storei64_release(&arena->purge_expire_extend, (mi_msecs_t)0);
+    }
   }
   return vinfo.any_purged;
 }

src/bitmap.c

@@ -1332,18 +1332,16 @@ bool _mi_bitmap_forall_set_ranges(mi_bitmap_t* bitmap, mi_forall_set_fun_t* visi
       for (size_t j = 0; j < MI_BCHUNK_FIELDS; j++) {
         const size_t base_idx = (chunk_idx*MI_BCHUNK_BITS) + (j*MI_BFIELD_BITS);
         mi_bfield_t b = mi_atomic_load_relaxed(&chunk->bfields[j]);
-        size_t bshift = 0;
         size_t bidx;
-        while (mi_bfield_find_least_bit(b, &bidx)) {
+        while (mi_bfield_find_least_bit(b, &bidx)) {          
-          b >>= bidx;
+          const size_t rng = mi_ctz(~(b>>bidx)); // all the set bits from bidx
-          bshift += bidx;
+          mi_assert_internal(rng>=1 && rng<=MI_BFIELD_BITS);
-          const size_t rng = mi_ctz(~b); // all the set bits from bidx
+          const size_t idx = base_idx + bidx;
-          mi_assert_internal(rng>=1);
+          mi_assert_internal((idx % MI_BFIELD_BITS) + rng <= MI_BFIELD_BITS);
-          const size_t idx = base_idx + bshift + bidx;
+          mi_assert_internal((idx / MI_BCHUNK_BITS) < mi_bitmap_chunk_count(bitmap));
           if (!visit(idx, rng, arena, arg)) return false;
-          // skip rng
+          // clear rng bits in b
-          b >>= rng;
+          b = b & ~mi_bfield_mask(rng, bidx);          
-          bshift += rng;
         }
       }
     }

test/test-stress.c

@@ -305,6 +305,7 @@ int main(int argc, char** argv) {
   #endif
   #if !defined(NDEBUG) && !defined(USE_STD_MALLOC)
     // mi_option_set(mi_option_arena_reserve, 32 * 1024 /* in kib = 32MiB */);
+    mi_option_set(mi_option_purge_delay,10);
   #endif
   #ifndef USE_STD_MALLOC
     mi_stats_reset();
@@ -353,8 +354,8 @@ int main(int argc, char** argv) {
   mi_debug_show_arenas(true,false,false);
   #else
   //mi_collect(true);
-  //mi_debug_show_arenas(true,false,false);
+  mi_debug_show_arenas(true,false,false);
-  // mi_stats_print(NULL);
+  mi_stats_print(NULL);
   #endif
 #else
   mi_stats_print(NULL);  // so we see rss/commit/elapsed