如果服务器收到的RPC超过这个最大数量，它会把多余的RPC排队，直到有空闲的调用执行者线程可以执行rpc。
If the server receives more than the maximum number, it simply queues the additional RPCs until a free call executor thread is available to execute the RPC.
多余的进程保持空闲，以处理传入的请求，这缩短了启动延迟。
Spare processes are kept idle to handle incoming requests, which reduces the start-up latency.
如果重新分配的块小于原来的块，那么把它分割开，多余的块返回给空闲树，请求的块返回给调用者。
If the size of the reallocated block is smaller than the original block, the block is split and the extra block is returned to the free tree with the required size block being returned to the caller.
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