从HotSpot
JVM来源：
// Minimum region size; we won't go lower than that. // We might want to decrease this in the future, to deal with small // heaps a bit more efficiently. static const size_t MIN_REGION_SIZE = 1024 * 1024; // Maximum region size; we don't go higher than that. There's a good // reason for having an upper bound. We don't want regions to get too // large, otherwise cleanup's effectiveness would decrease as there // will be fewer opportunities to find totally empty regions after // marking. static const size_t MAX_REGION_SIZE = 32 * 1024 * 1024; // The automatic region size calculation will try to have around this // many regions in the heap (based on the min heap size). static const size_t TARGET_REGION_NUMBER = 2048;
MIN_REGION_SIZE
（1MB）和MAX_REGION_SIZE
（32MB）是硬限制；TARGET_REGION_NUMBER
如果在JVM选项中未指定默认区域大小，则该提示仅用于计算默认区域大小。实际数字可能超过此值。
