revise the segment map to only apply to OS allocated segments and reduce the .BSS footprint

src/arena.c

@@ -36,7 +36,7 @@ The arena allocation needs to be thread safe and we use an atomic bitmap to allo
 typedef uintptr_t mi_block_info_t;
 #define MI_ARENA_BLOCK_SIZE   (MI_SEGMENT_SIZE)        // 64MiB  (must be at least MI_SEGMENT_ALIGN)
 #define MI_ARENA_MIN_OBJ_SIZE (MI_ARENA_BLOCK_SIZE/2)  // 32MiB
-#define MI_MAX_ARENAS         (255)                    // Limited as the reservation exponentially increases (and takes up .bss)
+#define MI_MAX_ARENAS         (132)                    // Limited as the reservation exponentially increases (and takes up .bss)
 
 // A memory arena descriptor
 typedef struct mi_arena_s {
@@ -735,7 +735,7 @@ void _mi_arena_unsafe_destroy_all(mi_stats_t* stats) {
 bool _mi_arena_contains(const void* p) {
   const size_t max_arena = mi_atomic_load_relaxed(&mi_arena_count);
   for (size_t i = 0; i < max_arena; i++) {
-    mi_arena_t* arena = mi_atomic_load_ptr_acquire(mi_arena_t, &mi_arenas[i]);
+    mi_arena_t* arena = mi_atomic_load_ptr_relaxed(mi_arena_t, &mi_arenas[i]);
     if (arena != NULL && arena->start <= (const uint8_t*)p && arena->start + mi_arena_block_size(arena->block_count) > (const uint8_t*)p) {
       return true;
     }

src/os.c

@@ -157,7 +157,8 @@ static void mi_os_prim_free(void* addr, size_t size, bool still_committed, mi_st
   _mi_stat_decrease(&stats->reserved, size);
 }
 
-void _mi_os_free_ex(void* addr, size_t size, bool still_committed, mi_memid_t memid, mi_stats_t* tld_stats) {
+void _mi_os_free_ex(void* addr, size_t size, bool still_committed, mi_memid_t memid, mi_stats_t* stats) {
+  if (stats == NULL) stats = &_mi_stats_main;
   if (mi_memkind_is_os(memid.memkind)) {
     size_t csize = _mi_os_good_alloc_size(size);
     void* base = addr;
@@ -171,10 +172,10 @@ void _mi_os_free_ex(void* addr, size_t size, bool still_committed, mi_memid_t me
     // free it
     if (memid.memkind == MI_MEM_OS_HUGE) {
       mi_assert(memid.is_pinned);
-      mi_os_free_huge_os_pages(base, csize, tld_stats);
+      mi_os_free_huge_os_pages(base, csize, stats);
     }
     else {
-      mi_os_prim_free(base, csize, still_committed, tld_stats);
+      mi_os_prim_free(base, csize, still_committed, stats);
     }
   }
   else {
@@ -183,8 +184,9 @@ void _mi_os_free_ex(void* addr, size_t size, bool still_committed, mi_memid_t me
   }
 }
 
-void  _mi_os_free(void* p, size_t size, mi_memid_t memid, mi_stats_t* tld_stats) {
+void  _mi_os_free(void* p, size_t size, mi_memid_t memid, mi_stats_t* stats) {
-  _mi_os_free_ex(p, size, true, memid, tld_stats);
+  if (stats == NULL) stats = &_mi_stats_main;
+  _mi_os_free_ex(p, size, true, memid, stats);
 }
 
 
@@ -299,6 +301,7 @@ static void* mi_os_prim_alloc_aligned(size_t size, size_t alignment, bool commit
 void* _mi_os_alloc(size_t size, mi_memid_t* memid, mi_stats_t* stats) {
   *memid = _mi_memid_none();
   if (size == 0) return NULL;
+  if (stats == NULL) stats = &_mi_stats_main;
   size = _mi_os_good_alloc_size(size);
   bool os_is_large = false;
   bool os_is_zero  = false;
@@ -314,6 +317,7 @@ void* _mi_os_alloc_aligned(size_t size, size_t alignment, bool commit, bool allo
   MI_UNUSED(&_mi_os_get_aligned_hint); // suppress unused warnings
   *memid = _mi_memid_none();
   if (size == 0) return NULL;
+  if (stats == NULL) stats = &_mi_stats_main;
   size = _mi_os_good_alloc_size(size);
   alignment = _mi_align_up(alignment, _mi_os_page_size());
 
@@ -342,6 +346,7 @@ void* _mi_os_alloc_aligned_at_offset(size_t size, size_t alignment, size_t offse
   mi_assert(offset <= size);
   mi_assert((alignment % _mi_os_page_size()) == 0);
   *memid = _mi_memid_none();
+  if (stats == NULL) stats = &_mi_stats_main;
   if (offset > MI_SEGMENT_SIZE) return NULL;
   if (offset == 0) {
     // regular aligned allocation

src/segment-map.c

@@ -16,140 +16,112 @@ terms of the MIT license. A copy of the license can be found in the file
 #include "mimalloc/internal.h"
 #include "mimalloc/atomic.h"
 
-#if (MI_INTPTR_SIZE>=8) && MI_TRACK_ASAN
+// Reduce total address space to reduce .bss  (due to the `mi_segment_map`)
-#define MI_MAX_ADDRESS    ((size_t)140 << 40) // 140TB (see issue #881)
+#if (MI_INTPTR_SIZE > 4) && MI_TRACK_ASAN
-#elif (MI_INTPTR_SIZE >= 8)
+#define MI_SEGMENT_MAP_MAX_ADDRESS    (128*1024ULL*MI_GiB)  // 128 TiB  (see issue #881)
-#define MI_MAX_ADDRESS    ((size_t)40 << 40)  // 40TB (to include huge page areas)
+#elif (MI_INTPTR_SIZE > 4)
+#define MI_SEGMENT_MAP_MAX_ADDRESS    (48*1024ULL*MI_GiB)   // 48 TiB
 #else
-#define MI_MAX_ADDRESS    ((size_t)2 << 30)   // 2Gb
+#define MI_SEGMENT_MAP_MAX_ADDRESS    (MAX_UINT32)
 #endif
 
-#define MI_SEGMENT_MAP_BITS  (MI_MAX_ADDRESS / MI_SEGMENT_SIZE)
+#define MI_SEGMENT_MAP_PART_SIZE      (MI_INTPTR_SIZE*MI_KiB - 128)      // 128 > sizeof(mi_memid_t) ! 
-#define MI_SEGMENT_MAP_SIZE  (MI_SEGMENT_MAP_BITS / 8)
+#define MI_SEGMENT_MAP_PART_BITS      (8*MI_SEGMENT_MAP_PART_SIZE)
-#define MI_SEGMENT_MAP_WSIZE (MI_SEGMENT_MAP_SIZE / MI_INTPTR_SIZE)
+#define MI_SEGMENT_MAP_PART_ENTRIES   (MI_SEGMENT_MAP_PART_SIZE / MI_INTPTR_SIZE)
+#define MI_SEGMENT_MAP_PART_BIT_SPAN  (MI_SEGMENT_ALIGN)
+#define MI_SEGMENT_MAP_PART_SPAN      (MI_SEGMENT_MAP_PART_BITS * MI_SEGMENT_MAP_PART_BIT_SPAN)
+#define MI_SEGMENT_MAP_MAX_PARTS      ((MI_SEGMENT_MAP_MAX_ADDRESS / MI_SEGMENT_MAP_PART_SPAN) + 1)
 
-static _Atomic(uintptr_t) mi_segment_map[MI_SEGMENT_MAP_WSIZE + 1];  // 2KiB per TB with 64MiB segments
+// A part of the segment map.
+typedef struct mi_segmap_part_s {
+  mi_memid_t memid;
+  _Atomic(uintptr_t) map[MI_SEGMENT_MAP_PART_ENTRIES];
+} mi_segmap_part_t;
 
-static size_t mi_segment_map_index_of(const mi_segment_t* segment, size_t* bitidx) {
+// Allocate parts on-demand to reduce .bss footprint
+_Atomic(mi_segmap_part_t*) mi_segment_map[MI_SEGMENT_MAP_MAX_PARTS]; // = { NULL, .. }
+
+
+static mi_segmap_part_t* mi_segment_map_index_of(const mi_segment_t* segment, bool create_on_demand, size_t* idx, size_t* bitidx) {
   // note: segment can be invalid or NULL.
   mi_assert_internal(_mi_ptr_segment(segment + 1) == segment); // is it aligned on MI_SEGMENT_SIZE?
-  if ((uintptr_t)segment >= MI_MAX_ADDRESS) {
+  *idx = 0;
   *bitidx = 0;  
-    return MI_SEGMENT_MAP_WSIZE;
+  if ((uintptr_t)segment >= MI_SEGMENT_MAP_MAX_ADDRESS) return NULL;
+  const uintptr_t segindex = ((uintptr_t)segment) / MI_SEGMENT_MAP_PART_SPAN;
+  if (segindex >= MI_SEGMENT_MAP_MAX_PARTS) return NULL;
+  mi_segmap_part_t* part = mi_atomic_load_ptr_relaxed(mi_segmap_part_t*, &mi_segment_map[segindex]);
+
+  // allocate on demand to reduce .bss footprint
+  if (part == NULL) {
+    if (!create_on_demand) return NULL;
+    mi_memid_t memid;
+    part = (mi_segmap_part_t*)_mi_os_alloc(sizeof(mi_segmap_part_t), &memid, NULL);
+    if (part == NULL) return NULL;
+    mi_segmap_part_t* expected = NULL;
+    if (!mi_atomic_cas_ptr_strong_release(mi_segmap_part_t, &mi_segment_map[segindex], &expected, part)) {
+      _mi_os_free(part, sizeof(mi_segmap_part_t), memid, NULL);
+      part = expected;
+      if (part == NULL) return NULL;
     }
-  else {
-    const uintptr_t segindex = ((uintptr_t)segment) / MI_SEGMENT_SIZE;
-    *bitidx = segindex % MI_INTPTR_BITS;
-    const size_t mapindex = segindex / MI_INTPTR_BITS;
-    mi_assert_internal(mapindex < MI_SEGMENT_MAP_WSIZE);
-    return mapindex;
   }
+  mi_assert(part != NULL);
+  const uintptr_t offset = ((uintptr_t)segment) % MI_SEGMENT_MAP_PART_SPAN;
+  const uintptr_t bitofs = offset / MI_SEGMENT_MAP_PART_BIT_SPAN;
+  *idx = bitofs / MI_INTPTR_BITS;
+  *bitidx = bitofs % MI_INTPTR_BITS;
+  return part;
 }
 
 void _mi_segment_map_allocated_at(const mi_segment_t* segment) {
+  if (segment->memid.memkind == MI_MEM_ARENA) return; // we lookup segments first in the arena's and don't need the segment map
+  size_t index;
   size_t bitidx;
-  size_t index = mi_segment_map_index_of(segment, &bitidx);
+  mi_segmap_part_t* part = mi_segment_map_index_of(segment, true /* alloc map if needed */, &index, &bitidx);
-  mi_assert_internal(index <= MI_SEGMENT_MAP_WSIZE);
+  if (part == NULL) return; // outside our address range..
-  if (index==MI_SEGMENT_MAP_WSIZE) return;
+  uintptr_t mask = mi_atomic_load_relaxed(&part->map[index]);
-  uintptr_t mask = mi_atomic_load_relaxed(&mi_segment_map[index]);
   uintptr_t newmask;
   do {
     newmask = (mask | ((uintptr_t)1 << bitidx));
-  } while (!mi_atomic_cas_weak_release(&mi_segment_map[index], &mask, newmask));
+  } while (!mi_atomic_cas_weak_release(&part->map[index], &mask, newmask));
 }
 
 void _mi_segment_map_freed_at(const mi_segment_t* segment) {
+  if (segment->memid.memkind == MI_MEM_ARENA) return;
+  size_t index;
   size_t bitidx;
-  size_t index = mi_segment_map_index_of(segment, &bitidx);
+  mi_segmap_part_t* part = mi_segment_map_index_of(segment, false /* don't alloc if not present */, &index, &bitidx);
-  mi_assert_internal(index <= MI_SEGMENT_MAP_WSIZE);
+  if (part == NULL) return; // outside our address range..
-  if (index == MI_SEGMENT_MAP_WSIZE) return;
+  uintptr_t mask = mi_atomic_load_relaxed(&part->map[index]);
-  uintptr_t mask = mi_atomic_load_relaxed(&mi_segment_map[index]);
   uintptr_t newmask;
   do {
     newmask = (mask & ~((uintptr_t)1 << bitidx));
-  } while (!mi_atomic_cas_weak_release(&mi_segment_map[index], &mask, newmask));
+  } while (!mi_atomic_cas_weak_release(&part->map[index], &mask, newmask));
 }
 
 // Determine the segment belonging to a pointer or NULL if it is not in a valid segment.
 static mi_segment_t* _mi_segment_of(const void* p) {
   if (p == NULL) return NULL;
   mi_segment_t* segment = _mi_ptr_segment(p);  // segment can be NULL  
+  size_t index;
   size_t bitidx;
-  size_t index = mi_segment_map_index_of(segment, &bitidx);
+  mi_segmap_part_t* part = mi_segment_map_index_of(segment, false /* dont alloc if not present */, &index, &bitidx);
-  // fast path: for any pointer to valid small/medium/large object or first MI_SEGMENT_SIZE in huge
+  if (part == NULL) return NULL;  
-  const uintptr_t mask = mi_atomic_load_relaxed(&mi_segment_map[index]);
+  const uintptr_t mask = mi_atomic_load_relaxed(&part->map[index]);
   if mi_likely((mask & ((uintptr_t)1 << bitidx)) != 0) {
+    bool cookie_ok = (_mi_ptr_cookie(segment) == segment->cookie);
+    mi_assert_internal(cookie_ok); MI_UNUSED(cookie_ok);
     return segment; // yes, allocated by us
   }
-  if (index==MI_SEGMENT_MAP_WSIZE) return NULL;
-
-  // TODO: maintain max/min allocated range for efficiency for more efficient rejection of invalid pointers?
-
-  // search downwards for the first segment in case it is an interior pointer
-  // could be slow but searches in MI_INTPTR_SIZE * MI_SEGMENT_SIZE (512MiB) steps trough
-  // valid huge objects
-  // note: we could maintain a lowest index to speed up the path for invalid pointers?
-  size_t lobitidx;
-  size_t loindex;
-  uintptr_t lobits = mask & (((uintptr_t)1 << bitidx) - 1);
-  if (lobits != 0) {
-    loindex = index;
-    lobitidx = mi_bsr(lobits);    // lobits != 0
-  }
-  else if (index == 0) {
   return NULL;
-  }
-  else {
-    mi_assert_internal(index > 0);
-    uintptr_t lomask = mask;
-    loindex = index;
-    do {
-      loindex--;  
-      lomask = mi_atomic_load_relaxed(&mi_segment_map[loindex]);      
-    } while (lomask != 0 && loindex > 0);
-    if (lomask == 0) return NULL;
-    lobitidx = mi_bsr(lomask);    // lomask != 0
-  }
-  mi_assert_internal(loindex < MI_SEGMENT_MAP_WSIZE);
-  // take difference as the addresses could be larger than the MAX_ADDRESS space.
-  size_t diff = (((index - loindex) * (8*MI_INTPTR_SIZE)) + bitidx - lobitidx) * MI_SEGMENT_SIZE;
-  segment = (mi_segment_t*)((uint8_t*)segment - diff);
-
-  if (segment == NULL) return NULL;
-  mi_assert_internal((void*)segment < p);
-  bool cookie_ok = (_mi_ptr_cookie(segment) == segment->cookie);
-  mi_assert_internal(cookie_ok);
-  if mi_unlikely(!cookie_ok) return NULL;
-  if (((uint8_t*)segment + mi_segment_size(segment)) <= (uint8_t*)p) return NULL; // outside the range
-  mi_assert_internal(p >= (void*)segment && (uint8_t*)p < (uint8_t*)segment + mi_segment_size(segment));
-  return segment;
 }
 
 // Is this a valid pointer in our heap?
 static bool mi_is_valid_pointer(const void* p) {
-  return ((_mi_segment_of(p) != NULL) || (_mi_arena_contains(p)));
+  // first check if it is in an arena, then check if it is OS allocated
+  return (_mi_arena_contains(p) || _mi_segment_of(p) != NULL);
 }
 
 mi_decl_nodiscard mi_decl_export bool mi_is_in_heap_region(const void* p) mi_attr_noexcept {
   return mi_is_valid_pointer(p);
 }
-
-/*
-// Return the full segment range belonging to a pointer
-static void* mi_segment_range_of(const void* p, size_t* size) {
-  mi_segment_t* segment = _mi_segment_of(p);
-  if (segment == NULL) {
-    if (size != NULL) *size = 0;
-    return NULL;
-  }
-  else {
-    if (size != NULL) *size = segment->segment_size;
-    return segment;
-  }
-  mi_assert_expensive(page == NULL || mi_segment_is_valid(_mi_page_segment(page),tld));
-  mi_assert_internal(page == NULL || (mi_segment_page_size(_mi_page_segment(page)) - (MI_SECURE == 0 ? 0 : _mi_os_page_size())) >= block_size);
-  mi_reset_delayed(tld);
-  mi_assert_internal(page == NULL || mi_page_not_in_queue(page, tld));
-  return page;
-}
-*/

test/test-stress.c

@@ -258,7 +258,7 @@ int main(int argc, char** argv) {
   #ifdef HEAP_WALK
     mi_option_enable(mi_option_visit_abandoned);    
   #endif
-  #ifndef NDBEBUG
+  #ifndef NDEBUG
     mi_option_set(mi_option_arena_reserve, 32 * 1024 /* in kib = 32MiB */);
   #endif
   #ifndef USE_STD_MALLOC