[REJECTREQUEST]system busy, start flow control for a while

[guyu0000]

现象：

1. 运行一段时间后客户端一直报这个错误，只有重启broker才能恢复
2. 未重启前，在store目录看到有两个commitLog，重启完后，那两个commitLog没了
3. watch org.apache.rocketmq.store.DefaultMessageStore isTransientStorePoolDeficient 发现结果一直为 false
   源码：

//org.apache.rocketmq.store.TransientStorePool
public int remainBufferNumbs() {
    if (storeConfig.isTransientStorePoolEnable()) {
        return availableBuffers.size(); //返回 0，说明buffer没有了
    }
    return Integer.MAX_VALUE;
}
//归还buffer
public void returnBuffer(ByteBuffer byteBuffer) {
    byteBuffer.position(0);
    byteBuffer.limit(fileSize);
    this.availableBuffers.offerFirst(byteBuffer);
}
//org.apache.rocketmq.store.MappedFile
public int commit(final int commitLeastPages) {
//...
	if (writeBuffer != null && this.transientStorePool != null && this.fileSize == this.committedPosition.get()) {
	    this.transientStorePool.returnBuffer(writeBuffer);
	    this.writeBuffer = null;
	}
//...
}

请教下：
想确认，从现象、源码 看是不是没有归还buffer？MappedFile是不是没有commit到？一般什么情况下会导致，buffer的可用数一直为 0

---

版本：4.4.0
配置：

brokerName = broker-a
brokerId = 0
brokerRole = ASYNC_MASTER
flushDiskType = ASYNC_FLUSH
autoCreateTopicEnable=false
autoCreateSubscriptionGroup=false
sendMessageThreadPoolNums=64
useReentrantLockWhenPutMessage=true
traceTopicEnable=true
slaveReadEnable=true
waitTimeMillsInSendQueue=500
messageDelayLevel=1s 5s 10s 30s 1m 5m 10m 30m 1h 2h
transientStorePoolEnable=true
osPageCacheBusyTimeOutMills=1500
transientStorePoolSize=2
#其他默认配置

机器：8C16G
主要JVM参数: -Xmx8g -Xms8g -Xmn4g

[guyu0000]

@RongtongJin 大佬 忙看看？