Remove hard_limit_for_bookkeeping (#77480)

As it turns out, it's not so easy to set aside a hard limit for the GC's bookkeeping, because some regions will be partially comitted and so will need more bookkeeping information as a percentage.

So this removes the hard_limit_for_bookkeeping and associated fields, and instead commits memory for the mark array eagerly, even if BGC is not in progress.

The issue is that GC needs at least one free region, and it needs the mark array committed. So when it tries to get a region at the end, and we cannot commit the mark array, we cannot actually get a free region. Currently we AV in this case, but there really isn't a good option to recover at this point. So it's better to keep the mark array committed and perhaps fail with an OOM exception.

src/coreclr/gc/gc.cpp

@@ -2336,9 +2336,6 @@ size_t      gc_heap::heap_hard_limit_oh[total_oh_count];
 
 size_t      gc_heap::regions_range = 0;
 
-size_t      gc_heap::heap_hard_limit_for_heap = 0;
-size_t      gc_heap::heap_hard_limit_for_bookkeeping = 0;
-
 #endif //USE_REGIONS
 
 bool        affinity_config_specified_p = false;
@@ -6956,34 +6953,16 @@ bool gc_heap::virtual_commit (void* address, size_t size, int bucket, int h_numb
 
         if (heap_hard_limit_oh[soh] != 0)
         {
-#ifdef USE_REGIONS
-            assert (heap_hard_limit_for_heap == 0);
-            assert (heap_hard_limit_for_bookkeeping == 0);
-#endif //USE_REGIONS
             if ((bucket < total_oh_count) && (committed_by_oh[bucket] + size) > heap_hard_limit_oh[bucket])
             {
                 exceeded_p = true;
             }
         }
         else
         {
-            size_t base;
-            size_t limit;
-#ifdef USE_REGIONS
-            if (h_number < 0)
-            {
-                base = current_total_committed_bookkeeping;
-                limit = heap_hard_limit_for_bookkeeping;
-            }
-            else
-            {
-                base = current_total_committed - current_total_committed_bookkeeping;
-                limit = heap_hard_limit_for_heap;
-            }
-#else
-            base = current_total_committed;
-            limit = heap_hard_limit;
-#endif //USE_REGIONS
+            size_t base = current_total_committed;
+            size_t limit = heap_hard_limit;
+
             if ((base + size) > limit)
             {
                 dprintf (1, ("%zd + %zd = %zd > limit %zd ", base, size, (base + size), limit));
@@ -11339,12 +11318,6 @@ void gc_heap::clear_region_info (heap_segment* region)
                         seg_deleted);
 
     bgc_verify_mark_array_cleared (region);
-
-    if (dt_high_memory_load_p())
-    {
-        decommit_mark_array_by_seg (region);
-        region->flags &= ~(heap_segment_flags_ma_committed);
-    }
 #endif //BACKGROUND_GC
 }
 
@@ -13671,26 +13644,6 @@ HRESULT gc_heap::initialize_gc (size_t soh_segment_size,
 #endif //BACKGROUND_GC
 #endif //WRITE_WATCH
 
-#ifdef USE_REGIONS
-    if (gc_heap::heap_hard_limit && gc_heap::heap_hard_limit_oh[soh] == 0)
-    {
-        size_t gc_region_size = (size_t)1 << min_segment_size_shr;
-        size_t sizes[total_bookkeeping_elements];
-        size_t bookkeeping_size_per_region = 0;
-        uint8_t* temp_lowest_address = (uint8_t*)gc_region_size;
-        gc_heap::get_card_table_element_sizes(temp_lowest_address, temp_lowest_address + gc_region_size, sizes);
-        for (int i = 0; i < total_bookkeeping_elements; i++)
-        {
-            bookkeeping_size_per_region += sizes[i];
-        }
-        size_t total_size_per_region = gc_region_size + bookkeeping_size_per_region;
-        size_t max_region_count = gc_heap::heap_hard_limit / total_size_per_region; // implictly rounded down
-        gc_heap::heap_hard_limit_for_heap = max_region_count * gc_region_size;
-        gc_heap::heap_hard_limit_for_bookkeeping = max_region_count * bookkeeping_size_per_region;
-        dprintf (REGIONS_LOG, ("bookkeeping_size_per_region = %zd", bookkeeping_size_per_region));
-    }
-#endif //USE_REGIONS
-
 #ifdef BACKGROUND_GC
     // leave the first page to contain only segment info
     // because otherwise we could need to revisit the first page frequently in
@@ -14450,6 +14403,8 @@ gc_heap::init_gc_heap (int h_number)
 #endif //CARD_BUNDLE
 
 #ifdef BACKGROUND_GC
+    background_saved_highest_address = nullptr;
+    background_saved_lowest_address = nullptr;
     if (gc_can_use_concurrent)
         mark_array = translate_mark_array (card_table_mark_array (&g_gc_card_table[card_word (card_of (g_gc_lowest_address))]));
     else
@@ -20370,20 +20325,17 @@ bool gc_heap::try_get_new_free_region()
 bool gc_heap::init_table_for_region (int gen_number, heap_segment* region)
 {
 #ifdef BACKGROUND_GC
-        if (is_bgc_in_progress())
+        dprintf (GC_TABLE_LOG, ("new seg %Ix, mark_array is %Ix",
+            heap_segment_mem (region), mark_array));
+        if (((region->flags & heap_segment_flags_ma_committed) == 0) &&
+            !commit_mark_array_new_seg (__this, region))
         {
-            dprintf (GC_TABLE_LOG, ("new seg %p, mark_array is %p",
-                heap_segment_mem (region), mark_array));
-            if (((region->flags & heap_segment_flags_ma_committed) == 0) &&
-                !commit_mark_array_new_seg (__this, region))
-            {
-                dprintf (GC_TABLE_LOG, ("failed to commit mark array for the new region %p-%p",
-                    get_region_start (region), heap_segment_reserved (region)));
+            dprintf (GC_TABLE_LOG, ("failed to commit mark array for the new region %Ix-%Ix",
+                get_region_start (region), heap_segment_reserved (region)));
 
-                // We don't have memory to commit the mark array so we cannot use the new region.
-                global_region_allocator.delete_region (get_region_start (region));
-                return false;
-            }
+            // We don't have memory to commit the mark array so we cannot use the new region.
+            global_region_allocator.delete_region (get_region_start (region));
+            return false;
         }
         if ((region->flags & heap_segment_flags_ma_committed) != 0)
         {

src/coreclr/gc/gcpriv.h

@@ -4115,12 +4115,6 @@ class gc_heap
     PER_HEAP_ISOLATED
     size_t heap_hard_limit_oh[total_oh_count];
 
-    PER_HEAP_ISOLATED
-    size_t heap_hard_limit_for_heap;
-
-    PER_HEAP_ISOLATED
-    size_t heap_hard_limit_for_bookkeeping;
-
     PER_HEAP_ISOLATED
     CLRCriticalSection check_commit_cs;