Make some region parameters configurable (#50603)

src/coreclr/gc/gc.cpp

@@ -40344,7 +40344,12 @@ HRESULT GCHeap::Initialize()
 #ifdef MULTIPLE_HEAPS
     gc_heap::soh_segment_size /= 4;
 #endif //MULTIPLE_HEAPS
-    gc_heap::min_segment_size_shr = index_of_highest_set_bit (REGION_SIZE);
+    size_t gc_region_size = (size_t)GCConfig::GetGCRegionsSize();
+    if (!power_of_two_p(gc_region_size) || ((gc_region_size * nhp * 19) > gc_heap::regions_range))
+    {
+        return E_INVALIDARG;
+    }
+    gc_heap::min_segment_size_shr = index_of_highest_set_bit (gc_region_size);
 #else
     gc_heap::min_segment_size_shr = index_of_highest_set_bit (gc_heap::min_segment_size);
 #endif //USE_REGIONS

src/coreclr/gc/gcconfig.h

@@ -102,7 +102,8 @@ public:
     INT_CONFIG   (GCHeapHardLimit,        "GCHeapHardLimit",        "System.GC.HeapHardLimit",        0,                 "Specifies a hard limit for the GC heap")                                                 \
     INT_CONFIG   (GCHeapHardLimitPercent, "GCHeapHardLimitPercent", "System.GC.HeapHardLimitPercent", 0,                 "Specifies the GC heap usage as a percentage of the total memory")                        \
     INT_CONFIG   (GCTotalPhysicalMemory,  "GCTotalPhysicalMemory",  NULL,                             0,                 "Specifies what the GC should consider to be total physical memory")                      \
-    INT_CONFIG   (GCRegionsRange,         "GCRegionsRange",         NULL,                             0,                 "Specifies the range for the GC heap")                                                    \
+    INT_CONFIG   (GCRegionsRange,         "GCRegionsRange",         NULL,                             274877906944L,     "Specifies the range for the GC heap")                                                    \
+    INT_CONFIG   (GCRegionsSize,          "GCRegionsSize",          NULL,                             4194304,           "Specifies the size for a basic GC region")                                               \
     STRING_CONFIG(LogFile,                "GCLogFile",              NULL,                                                "Specifies the name of the GC log file")                                                  \
     STRING_CONFIG(ConfigLogFile,          "GCConfigLogFile",        NULL,                                                "Specifies the name of the GC config log file")                                           \
     INT_CONFIG   (BGCFLTuningEnabled,     "BGCFLTuningEnabled",     NULL,                             0,                 "Enables FL tuning")                                                                      \

src/coreclr/gc/gcpriv.h

@@ -5278,8 +5278,6 @@ public:
 // and free_large_regions. These decommitted regions will be returned to region_allocator which
 // mark the space as free blocks.
 // 
-// Make configs available to change these.
-#define REGION_SIZE ((size_t)4 * 1024 * 1024)
 #define LARGE_REGION_FACTOR (8)
 
 #define region_alloc_free_bit (1 << (sizeof (uint32_t) * 8 - 1))