merge from dev-abandon

include/mimalloc.h

@@ -345,6 +345,7 @@ typedef enum mi_option_e {
   mi_option_arena_reserve,            // initial memory size in KiB for arena reservation (1GiB on 64-bit)
   mi_option_arena_purge_mult,         
   mi_option_purge_extend_delay,
+  mi_option_abandoned_reclaim_on_free,  // reclaim abandoned segments on a free
   _mi_option_last,
   // legacy option names
   mi_option_large_os_pages = mi_option_allow_large_os_pages,

include/mimalloc/internal.h

@@ -125,6 +125,10 @@ bool       _mi_arena_contains(const void* p);
 void       _mi_arena_collect(bool force_purge, mi_stats_t* stats);
 void       _mi_arena_unsafe_destroy_all(mi_stats_t* stats);
 
+bool          _mi_arena_segment_clear_abandoned(mi_memid_t memid);
+void          _mi_arena_segment_mark_abandoned(mi_memid_t memid);
+mi_segment_t* _mi_arena_segment_clear_abandoned_next(mi_arena_id_t* current_id, size_t* current_idx);
+
 // "segment-map.c"
 void       _mi_segment_map_allocated_at(const mi_segment_t* segment);
 void       _mi_segment_map_freed_at(const mi_segment_t* segment);
@@ -146,6 +150,7 @@ uint8_t*   _mi_segment_page_start(const mi_segment_t* segment, const mi_page_t*
 void       _mi_abandoned_reclaim_all(mi_heap_t* heap, mi_segments_tld_t* tld);
 void       _mi_abandoned_await_readers(void);
 void       _mi_abandoned_collect(mi_heap_t* heap, bool force, mi_segments_tld_t* tld);
+bool       _mi_segment_attempt_reclaim(mi_heap_t* heap, mi_segment_t* segment);
 
 // "page.c"
 void*      _mi_malloc_generic(mi_heap_t* heap, size_t size, bool zero, size_t huge_alignment)  mi_attr_noexcept mi_attr_malloc;

include/mimalloc/types.h

@@ -424,8 +424,6 @@ typedef struct mi_segment_s {
   mi_commit_mask_t  purge_mask;
   mi_commit_mask_t  commit_mask;
 
-  _Atomic(struct mi_segment_s*) abandoned_next;
-
   // from here is zero initialized
   struct mi_segment_s* next;            // the list of freed segments in the cache (must be first field, see `segment.c:mi_segment_init`)
 

src/alloc.c

@@ -401,13 +401,25 @@ static void mi_stat_huge_free(const mi_page_t* page) {
 // multi-threaded free (or free in huge block if compiled with MI_HUGE_PAGE_ABANDON)
 static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* block)
 {
+  // first see if the segment was abandoned and we can reclaim it
+  mi_segment_t* const segment = _mi_page_segment(page);
+  if (mi_option_is_enabled(mi_option_abandoned_reclaim_on_free) &&
+      mi_atomic_load_relaxed(&segment->thread_id) == 0)
+  {
+    // the segment is abandoned, try to reclaim it into our heap
+    if (_mi_segment_attempt_reclaim(mi_prim_get_default_heap(), segment)) {
+      mi_assert_internal(_mi_prim_thread_id() == mi_atomic_load_relaxed(&segment->thread_id));
+      mi_free(block);  // recursively free as now it will be a local free in our heap
+      return;
+    }
+  }
+
   // The padding check may access the non-thread-owned page for the key values.
   // that is safe as these are constant and the page won't be freed (as the block is not freed yet).
   mi_check_padding(page, block);
   _mi_padding_shrink(page, block, sizeof(mi_block_t));       // for small size, ensure we can fit the delayed thread pointers without triggering overflow detection
 
   // huge page segments are always abandoned and can be freed immediately  
-  mi_segment_t* segment = _mi_page_segment(page);
   if (segment->kind == MI_SEGMENT_HUGE) {
     #if MI_HUGE_PAGE_ABANDON
     // huge page segments are always abandoned and can be freed immediately

src/arena.c

@@ -55,6 +55,7 @@ typedef struct mi_arena_s {
   mi_bitmap_field_t* blocks_dirty;        // are the blocks potentially non-zero?
   mi_bitmap_field_t* blocks_committed;    // are the blocks committed? (can be NULL for memory that cannot be decommitted)
   mi_bitmap_field_t* blocks_purge;        // blocks that can be (reset) decommitted. (can be NULL for memory that cannot be (reset) decommitted)
+  mi_bitmap_field_t* blocks_abandoned;    // blocks that start with an abandoned segment. (This crosses API's but it is convenient to have here)
   mi_bitmap_field_t  blocks_inuse[1];     // in-place bitmap of in-use blocks (of size `field_count`)
 } mi_arena_t;
 
@@ -94,7 +95,7 @@ bool _mi_arena_memid_is_suitable(mi_memid_t memid, mi_arena_id_t request_arena_i
     return mi_arena_id_is_suitable(memid.mem.arena.id, memid.mem.arena.is_exclusive, request_arena_id);
   }
   else {
-    return mi_arena_id_is_suitable(0, false, request_arena_id);
+    return mi_arena_id_is_suitable(_mi_arena_id_none(), false, request_arena_id);
   }
 }
 
@@ -730,6 +731,90 @@ bool _mi_arena_contains(const void* p) {
   return false;
 }
 
+/* -----------------------------------------------------------
+  Abandoned blocks/segments.
+  This is used to atomically abandon/reclaim segments 
+  (and crosses the arena API but it is convenient to have here).
+  Abandoned segments still have live blocks; they get reclaimed
+  when a thread frees in it, or when a thread needs a fresh
+  segment; these threads scan the abandoned segments through
+  the arena bitmaps.
+----------------------------------------------------------- */
+
+// reclaim a specific abandoned segment; `true` on success.
+bool _mi_arena_segment_clear_abandoned(mi_memid_t memid ) 
+{
+  if (memid.memkind != MI_MEM_ARENA) return true;  // not in an arena, consider it un-abandoned
+  size_t arena_idx;
+  size_t bitmap_idx;
+  mi_arena_memid_indices(memid, &arena_idx, &bitmap_idx);
+  mi_assert_internal(arena_idx < MI_MAX_ARENAS);
+  mi_arena_t* arena = mi_atomic_load_ptr_acquire(mi_arena_t, &mi_arenas[arena_idx]);
+  mi_assert_internal(arena != NULL);
+  bool was_abandoned = _mi_bitmap_unclaim(arena->blocks_abandoned, arena->field_count, 1, bitmap_idx);
+  // mi_assert_internal(was_abandoned);
+  mi_assert_internal(!was_abandoned || _mi_bitmap_is_claimed(arena->blocks_inuse, arena->field_count, 1, bitmap_idx));
+  //mi_assert_internal(arena->blocks_committed == NULL || _mi_bitmap_is_claimed(arena->blocks_committed, arena->field_count, 1, bitmap_idx));
+  return was_abandoned;
+}
+
+// mark a specific segment as abandoned
+void _mi_arena_segment_mark_abandoned(mi_memid_t memid) 
+{
+  if (memid.memkind != MI_MEM_ARENA) return;  // not in an arena
+  size_t arena_idx;
+  size_t bitmap_idx;
+  mi_arena_memid_indices(memid, &arena_idx, &bitmap_idx);
+  mi_assert_internal(arena_idx < MI_MAX_ARENAS);
+  mi_arena_t* arena = mi_atomic_load_ptr_acquire(mi_arena_t, &mi_arenas[arena_idx]);
+  mi_assert_internal(arena != NULL);
+  const bool was_unset = _mi_bitmap_claim(arena->blocks_abandoned, arena->field_count, 1, bitmap_idx, NULL);
+  MI_UNUSED_RELEASE(was_unset);
+  mi_assert_internal(was_unset);
+  mi_assert_internal(_mi_bitmap_is_claimed(arena->blocks_inuse, arena->field_count, 1, bitmap_idx));
+}
+
+// reclaim abandoned segments 
+mi_segment_t* _mi_arena_segment_clear_abandoned_next(mi_arena_id_t* previous_id, size_t* previous_idx ) 
+{
+  const int max_arena = (int)mi_atomic_load_relaxed(&mi_arena_count);
+  int arena_idx = *previous_id;
+  size_t field_idx = mi_bitmap_index_field(*previous_idx);
+  size_t bit_idx = mi_bitmap_index_bit_in_field(*previous_idx) + 1;
+  // visit arena's (from previous)
+  for( ; arena_idx < max_arena; arena_idx++, field_idx = 0, bit_idx = 0) {
+    mi_arena_t* arena = mi_atomic_load_ptr_acquire(mi_arena_t, &mi_arenas[arena_idx]);
+    if (arena != NULL) {
+      // visit the abandoned fields (starting at previous_idx)
+      for ( ; field_idx < arena->field_count; field_idx++, bit_idx = 0) {
+        mi_bitmap_field_t field = mi_atomic_load_relaxed(&arena->blocks_abandoned[field_idx]);
+        if mi_unlikely(field != 0) { // skip zero fields quickly
+          // visit each set bit in the field  (todo: maybe use `ctz` here?)
+          for ( ; bit_idx < MI_BITMAP_FIELD_BITS; bit_idx++) {
+            // pre-check if the bit is set
+            mi_bitmap_field_t mask = ((mi_bitmap_field_t)1 << bit_idx);
+            if mi_unlikely((field & mask) == mask) {
+              mi_bitmap_index_t bitmap_idx = mi_bitmap_index_create(field_idx, bit_idx);
+              // try to reclaim it atomically
+              if (_mi_bitmap_unclaim(arena->blocks_abandoned, arena->field_count, 1, bitmap_idx)) {
+                *previous_idx = bitmap_idx;
+                *previous_id = arena_idx;
+                mi_assert_internal(_mi_bitmap_is_claimed(arena->blocks_inuse, arena->field_count, 1, bitmap_idx));
+                //mi_assert_internal(arena->blocks_committed == NULL || _mi_bitmap_is_claimed(arena->blocks_committed, arena->field_count, 1, bitmap_idx));
+                return (mi_segment_t*)mi_arena_block_start(arena, bitmap_idx);
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+  // no more found
+  *previous_idx = 0;
+  *previous_id = 0;
+  return NULL;
+}
+
 
 /* -----------------------------------------------------------
   Add an arena.
@@ -763,13 +848,13 @@ static bool mi_manage_os_memory_ex2(void* start, size_t size, bool is_large, int
 
   const size_t bcount = size / MI_ARENA_BLOCK_SIZE;
   const size_t fields = _mi_divide_up(bcount, MI_BITMAP_FIELD_BITS);
-  const size_t bitmaps = (memid.is_pinned ? 2 : 4);
+  const size_t bitmaps = (memid.is_pinned ? 3 : 5);
   const size_t asize  = sizeof(mi_arena_t) + (bitmaps*fields*sizeof(mi_bitmap_field_t));
   mi_memid_t meta_memid;
   mi_arena_t* arena   = (mi_arena_t*)mi_arena_meta_zalloc(asize, &meta_memid, &_mi_stats_main); // TODO: can we avoid allocating from the OS?
   if (arena == NULL) return false;
 
-  // already zero'd due to os_alloc
+  // already zero'd due to zalloc
   // _mi_memzero(arena, asize);
   arena->id = _mi_arena_id_none();
   arena->memid = memid;
@@ -783,9 +868,11 @@ static bool mi_manage_os_memory_ex2(void* start, size_t size, bool is_large, int
   arena->is_large     = is_large;
   arena->purge_expire = 0;
   arena->search_idx   = 0;
+  // consequetive bitmaps
   arena->blocks_dirty     = &arena->blocks_inuse[fields];     // just after inuse bitmap
-  arena->blocks_committed = (arena->memid.is_pinned ? NULL : &arena->blocks_inuse[2*fields]); // just after dirty bitmap
-  arena->blocks_purge  = (arena->memid.is_pinned ? NULL : &arena->blocks_inuse[3*fields]); // just after committed bitmap  
+  arena->blocks_abandoned = &arena->blocks_inuse[2 * fields]; // just after dirty bitmap
+  arena->blocks_committed = (arena->memid.is_pinned ? NULL : &arena->blocks_inuse[3*fields]); // just after abandonde bitmap
+  arena->blocks_purge     = (arena->memid.is_pinned ? NULL : &arena->blocks_inuse[4*fields]); // just after committed bitmap
   // initialize committed bitmap?
   if (arena->blocks_committed != NULL && arena->memid.initially_committed) {
     memset((void*)arena->blocks_committed, 0xFF, fields*sizeof(mi_bitmap_field_t)); // cast to void* to avoid atomic warning

src/options.c

@@ -81,7 +81,7 @@ static mi_option_desc_t options[_mi_option_last] =
   { 100, UNINIT, MI_OPTION(os_tag) },                   // only apple specific for now but might serve more or less related purpose
   { 16,  UNINIT, MI_OPTION(max_errors) },               // maximum errors that are output
   { 16,  UNINIT, MI_OPTION(max_warnings) },             // maximum warnings that are output
-  { 8,   UNINIT, MI_OPTION(max_segment_reclaim)},       // max. number of segment reclaims from the abandoned segments per try.
+  { 16,  UNINIT, MI_OPTION(max_segment_reclaim)},       // max. number of segment reclaims from the abandoned segments per try.
   { 0,   UNINIT, MI_OPTION(destroy_on_exit)},           // release all OS memory on process exit; careful with dangling pointer or after-exit frees!
   #if (MI_INTPTR_SIZE>4)
   { 1024L * 1024L, UNINIT, MI_OPTION(arena_reserve) },  // reserve memory N KiB at a time
@@ -90,6 +90,7 @@ static mi_option_desc_t options[_mi_option_last] =
   #endif
   { 10,  UNINIT, MI_OPTION(arena_purge_mult) },        // purge delay multiplier for arena's
   { 1,   UNINIT, MI_OPTION_LEGACY(purge_extend_delay, decommit_extend_delay) },
+  { 1,   UNINIT, MI_OPTION(abandoned_reclaim_on_free) }, // reclaim an abandoned segment on a free
 };
 
 static void mi_option_init(mi_option_desc_t* desc);

src/segment.c

@@ -847,7 +847,6 @@ static mi_segment_t* mi_segment_os_alloc( size_t required, size_t page_alignment
   segment->commit_mask = commit_mask;
   segment->purge_expire = 0;
   mi_commit_mask_create_empty(&segment->purge_mask);
-  mi_atomic_store_ptr_release(mi_segment_t, &segment->abandoned_next, NULL);  // tsan
 
   mi_segments_track_size((long)(segment_size), tld);
   _mi_segment_map_allocated_at(segment);
@@ -1036,172 +1035,20 @@ Abandonment
 When threads terminate, they can leave segments with
 live blocks (reachable through other threads). Such segments
 are "abandoned" and will be reclaimed by other threads to
-reuse their pages and/or free them eventually
+reuse their pages and/or free them eventually. The
+`thread_id` of such segments is 0.
 
-We maintain a global list of abandoned segments that are
-reclaimed on demand. Since this is shared among threads
-the implementation needs to avoid the A-B-A problem on
-popping abandoned segments: <https://en.wikipedia.org/wiki/ABA_problem>
-We use tagged pointers to avoid accidentally identifying
-reused segments, much like stamped references in Java.
-Secondly, we maintain a reader counter to avoid resetting
-or decommitting segments that have a pending read operation.
-
-Note: the current implementation is one possible design;
-another way might be to keep track of abandoned segments
-in the arenas/segment_cache's. This would have the advantage of keeping
-all concurrent code in one place and not needing to deal
-with ABA issues. The drawback is that it is unclear how to
-scan abandoned segments efficiently in that case as they
-would be spread among all other segments in the arenas.
+When a block is freed in an abandoned segment, the segment
+is reclaimed into that thread.
 ----------------------------------------------------------- */
 
-// Use the bottom 20-bits (on 64-bit) of the aligned segment pointers
-// to put in a tag that increments on update to avoid the A-B-A problem.
-#define MI_TAGGED_MASK   MI_SEGMENT_MASK
-typedef uintptr_t        mi_tagged_segment_t;
-
-static mi_segment_t* mi_tagged_segment_ptr(mi_tagged_segment_t ts) {
-  return (mi_segment_t*)(ts & ~MI_TAGGED_MASK);
-}
-
-static mi_tagged_segment_t mi_tagged_segment(mi_segment_t* segment, mi_tagged_segment_t ts) {
-  mi_assert_internal(((uintptr_t)segment & MI_TAGGED_MASK) == 0);
-  uintptr_t tag = ((ts & MI_TAGGED_MASK) + 1) & MI_TAGGED_MASK;
-  return ((uintptr_t)segment | tag);
-}
-
-// This is a list of visited abandoned pages that were full at the time.
-// this list migrates to `abandoned` when that becomes NULL. The use of
-// this list reduces contention and the rate at which segments are visited.
-static mi_decl_cache_align _Atomic(mi_segment_t*)       abandoned_visited; // = NULL
-
-// The abandoned page list (tagged as it supports pop)
-static mi_decl_cache_align _Atomic(mi_tagged_segment_t) abandoned;         // = NULL
-
-// Maintain these for debug purposes (these counts may be a bit off)
+// Maintain these for debug purposes
 static mi_decl_cache_align _Atomic(size_t)abandoned_count;
-static mi_decl_cache_align _Atomic(size_t)           abandoned_visited_count;
 
-// We also maintain a count of current readers of the abandoned list
-// in order to prevent resetting/decommitting segment memory if it might
-// still be read.
-static mi_decl_cache_align _Atomic(size_t)           abandoned_readers; // = 0
 
-// Push on the visited list
-static void mi_abandoned_visited_push(mi_segment_t* segment) {
-  mi_assert_internal(segment->thread_id == 0);
-  mi_assert_internal(mi_atomic_load_ptr_relaxed(mi_segment_t,&segment->abandoned_next) == NULL);
-  mi_assert_internal(segment->next == NULL);
-  mi_assert_internal(segment->used > 0);
-  mi_segment_t* anext = mi_atomic_load_ptr_relaxed(mi_segment_t, &abandoned_visited);
-  do {
-    mi_atomic_store_ptr_release(mi_segment_t, &segment->abandoned_next, anext);
-  } while (!mi_atomic_cas_ptr_weak_release(mi_segment_t, &abandoned_visited, &anext, segment));
-  mi_atomic_increment_relaxed(&abandoned_visited_count);
-}
-
-// Move the visited list to the abandoned list.
-static bool mi_abandoned_visited_revisit(void)
-{
-  // quick check if the visited list is empty
-  if (mi_atomic_load_ptr_relaxed(mi_segment_t, &abandoned_visited) == NULL) return false;
-
-  // grab the whole visited list
-  mi_segment_t* first = mi_atomic_exchange_ptr_acq_rel(mi_segment_t, &abandoned_visited, NULL);
-  if (first == NULL) return false;
-
-  // first try to swap directly if the abandoned list happens to be NULL
-  mi_tagged_segment_t afirst;
-  mi_tagged_segment_t ts = mi_atomic_load_relaxed(&abandoned);
-  if (mi_tagged_segment_ptr(ts)==NULL) {
-    size_t count = mi_atomic_load_relaxed(&abandoned_visited_count);
-    afirst = mi_tagged_segment(first, ts);
-    if (mi_atomic_cas_strong_acq_rel(&abandoned, &ts, afirst)) {
-      mi_atomic_add_relaxed(&abandoned_count, count);
-      mi_atomic_sub_relaxed(&abandoned_visited_count, count);
-      return true;
-    }
-  }
-
-  // find the last element of the visited list: O(n)
-  mi_segment_t* last = first;
-  mi_segment_t* next;
-  while ((next = mi_atomic_load_ptr_relaxed(mi_segment_t, &last->abandoned_next)) != NULL) {
-    last = next;
-  }
-
-  // and atomically prepend to the abandoned list
-  // (no need to increase the readers as we don't access the abandoned segments)
-  mi_tagged_segment_t anext = mi_atomic_load_relaxed(&abandoned);
-  size_t count;
-  do {
-    count = mi_atomic_load_relaxed(&abandoned_visited_count);
-    mi_atomic_store_ptr_release(mi_segment_t, &last->abandoned_next, mi_tagged_segment_ptr(anext));
-    afirst = mi_tagged_segment(first, anext);
-  } while (!mi_atomic_cas_weak_release(&abandoned, &anext, afirst));
-  mi_atomic_add_relaxed(&abandoned_count, count);
-  mi_atomic_sub_relaxed(&abandoned_visited_count, count);
-  return true;
-}
-
-// Push on the abandoned list.
-static void mi_abandoned_push(mi_segment_t* segment) {
-  mi_assert_internal(segment->thread_id == 0);
-  mi_assert_internal(mi_atomic_load_ptr_relaxed(mi_segment_t, &segment->abandoned_next) == NULL);
-  mi_assert_internal(segment->next == NULL);
-  mi_assert_internal(segment->used > 0);
-  mi_tagged_segment_t next;
-  mi_tagged_segment_t ts = mi_atomic_load_relaxed(&abandoned);
-  do {
-    mi_atomic_store_ptr_release(mi_segment_t, &segment->abandoned_next, mi_tagged_segment_ptr(ts));
-    next = mi_tagged_segment(segment, ts);
-  } while (!mi_atomic_cas_weak_release(&abandoned, &ts, next));
-  mi_atomic_increment_relaxed(&abandoned_count);
-}
-
-// Wait until there are no more pending reads on segments that used to be in the abandoned list
-// called for example from `arena.c` before decommitting
+// legacy: Wait until there are no more pending reads on segments that used to be in the abandoned list
 void _mi_abandoned_await_readers(void) {
-  size_t n;
-  do {
-    n = mi_atomic_load_acquire(&abandoned_readers);
-    if (n != 0) mi_atomic_yield();
-  } while (n != 0);
-}
-
-// Pop from the abandoned list
-static mi_segment_t* mi_abandoned_pop(void) {
-  mi_segment_t* segment;
-  // Check efficiently if it is empty (or if the visited list needs to be moved)
-  mi_tagged_segment_t ts = mi_atomic_load_relaxed(&abandoned);
-  segment = mi_tagged_segment_ptr(ts);
-  if mi_likely(segment == NULL) {
-    if mi_likely(!mi_abandoned_visited_revisit()) { // try to swap in the visited list on NULL
-      return NULL;
-    }
-  }
-
-  // Do a pop. We use a reader count to prevent
-  // a segment to be decommitted while a read is still pending,
-  // and a tagged pointer to prevent A-B-A link corruption.
-  // (this is called from `region.c:_mi_mem_free` for example)
-  mi_atomic_increment_relaxed(&abandoned_readers);  // ensure no segment gets decommitted
-  mi_tagged_segment_t next = 0;
-  ts = mi_atomic_load_acquire(&abandoned);
-  do {
-    segment = mi_tagged_segment_ptr(ts);
-    if (segment != NULL) {
-      mi_segment_t* anext = mi_atomic_load_ptr_relaxed(mi_segment_t, &segment->abandoned_next);
-      next = mi_tagged_segment(anext, ts); // note: reads the segment's `abandoned_next` field so should not be decommitted
-    }
-  } while (segment != NULL && !mi_atomic_cas_weak_acq_rel(&abandoned, &ts, next));
-  mi_atomic_decrement_relaxed(&abandoned_readers);  // release reader lock
-  if (segment != NULL) {
-    mi_atomic_store_ptr_release(mi_segment_t, &segment->abandoned_next, NULL);
-    mi_atomic_decrement_relaxed(&abandoned_count);
-  }
-  return segment;
+  // nothing needed
 }
 
 /* -----------------------------------------------------------
@@ -1211,7 +1058,6 @@ static mi_segment_t* mi_abandoned_pop(void) {
 static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
   mi_assert_internal(segment->used == segment->abandoned);
   mi_assert_internal(segment->used > 0);
-  mi_assert_internal(mi_atomic_load_ptr_relaxed(mi_segment_t, &segment->abandoned_next) == NULL);
   mi_assert_internal(segment->abandoned_visits == 0);
   mi_assert_expensive(mi_segment_is_valid(segment,tld));
 
@@ -1235,9 +1081,8 @@ static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
   _mi_stat_increase(&tld->stats->segments_abandoned, 1);
   mi_segments_track_size(-((long)mi_segment_size(segment)), tld);
   segment->thread_id = 0;
-  mi_atomic_store_ptr_release(mi_segment_t, &segment->abandoned_next, NULL);
   segment->abandoned_visits = 1;   // from 0 to 1 to signify it is abandoned
-  mi_abandoned_push(segment);
+  _mi_arena_segment_mark_abandoned(segment->memid); mi_atomic_increment_relaxed(&abandoned_count);
 }
 
 void _mi_segment_page_abandon(mi_page_t* page, mi_segments_tld_t* tld) {
@@ -1318,7 +1163,6 @@ static bool mi_segment_check_free(mi_segment_t* segment, size_t slices_needed, s
 // Reclaim an abandoned segment; returns NULL if the segment was freed
 // set `right_page_reclaimed` to `true` if it reclaimed a page of the right `block_size` that was not full.
 static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap, size_t requested_block_size, bool* right_page_reclaimed, mi_segments_tld_t* tld) {
-  mi_assert_internal(mi_atomic_load_ptr_relaxed(mi_segment_t, &segment->abandoned_next) == NULL);
   mi_assert_expensive(mi_segment_is_valid(segment, tld));
   if (right_page_reclaimed != NULL) { *right_page_reclaimed = false; }
 
@@ -1378,10 +1222,23 @@ static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap,
   }
 }
 
+// attempt to reclaim a particular segment (called from multi threaded free `alloc.c:mi_free_block_mt`)
+bool _mi_segment_attempt_reclaim(mi_heap_t* heap, mi_segment_t* segment) {
+  if (mi_atomic_load_relaxed(&segment->thread_id) != 0) return false;  // it is not abandoned
+  if (_mi_arena_segment_clear_abandoned(segment->memid)) {  // atomically unabandon
+    mi_segment_t* res = mi_segment_reclaim(segment, heap, 0, NULL, &heap->tld->segments);
+    mi_assert_internal(res != NULL);
+    return (res != NULL);
+  }
+  return false;
+}
 
 void _mi_abandoned_reclaim_all(mi_heap_t* heap, mi_segments_tld_t* tld) {
   mi_segment_t* segment;
-  while ((segment = mi_abandoned_pop()) != NULL) {
+  mi_arena_id_t current_id = 0;
+  size_t        current_idx = 0;
+  while ((segment = _mi_arena_segment_clear_abandoned_next(&current_id, &current_idx)) != NULL) {
+    mi_atomic_decrement_relaxed(&abandoned_count);
     mi_segment_reclaim(segment, heap, 0, NULL, tld);
   }
 }
@@ -1390,8 +1247,12 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
 {
   *reclaimed = false;
   mi_segment_t* segment;
-  long max_tries = mi_option_get_clamp(mi_option_max_segment_reclaim, 8, 1024);     // limit the work to bound allocation times
-  while ((max_tries-- > 0) && ((segment = mi_abandoned_pop()) != NULL)) {
+  mi_arena_id_t current_id = 0;
+  size_t        current_idx = 0;
+  long max_tries = mi_option_get_clamp(mi_option_max_segment_reclaim, 0, 1024);     // limit the work to bound allocation times
+  while ((max_tries-- > 0) && ((segment = _mi_arena_segment_clear_abandoned_next(&current_id, &current_idx)) != NULL))
+  {
+    mi_atomic_decrement_relaxed(&abandoned_count);
     segment->abandoned_visits++;
     // todo: an arena exclusive heap will potentially visit many abandoned unsuitable segments
     // and push them into the visited list and use many tries. Perhaps we can skip non-suitable ones in a better way?
@@ -1417,8 +1278,9 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
     }
     else {
       // otherwise, push on the visited list so it gets not looked at too quickly again
-      mi_segment_try_purge(segment, true /* force? */, tld->stats); // force purge if needed as we may not visit soon again
-      mi_abandoned_visited_push(segment);
+      mi_segment_try_purge(segment, false /* true force? */, tld->stats); // force purge if needed as we may not visit soon again
+      mi_atomic_increment_relaxed(&abandoned_count);
+      _mi_arena_segment_mark_abandoned(segment->memid);
     }
   }
   return NULL;
@@ -1428,11 +1290,11 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
 void _mi_abandoned_collect(mi_heap_t* heap, bool force, mi_segments_tld_t* tld)
 {
   mi_segment_t* segment;
+  mi_arena_id_t current_id = 0;
+  size_t        current_idx = 0;
   int max_tries = (force ? 16*1024 : 1024); // limit latency  
-  if (force) {
-    mi_abandoned_visited_revisit(); 
-  }
-  while ((max_tries-- > 0) && ((segment = mi_abandoned_pop()) != NULL)) {
+  while ((max_tries-- > 0) && ((segment = _mi_arena_segment_clear_abandoned_next(&current_id,&current_idx)) != NULL)) {
+    mi_atomic_decrement_relaxed(&abandoned_count);
     mi_segment_check_free(segment,0,0,tld); // try to free up pages (due to concurrent frees)
     if (segment->used == 0) {
       // free the segment (by forced reclaim) to make it available to other threads.
@@ -1444,7 +1306,8 @@ void _mi_abandoned_collect(mi_heap_t* heap, bool force, mi_segments_tld_t* tld)
       // otherwise, purge if needed and push on the visited list
       // note: forced purge can be expensive if many threads are destroyed/created as in mstress.
       mi_segment_try_purge(segment, force, tld->stats);
-      mi_abandoned_visited_push(segment);
+      mi_atomic_increment_relaxed(&abandoned_count);
+      _mi_arena_segment_mark_abandoned(segment->memid);
     }
   }
 }