Hi, When defining my own TCP congestion control, I encountered this: BUILD_BUG_ON(sizeof(struct mytcp) > ICSK_CA_PRIV_SIZE); Every socket using my own congestion control has an instance of the struct mytcp, which stores per-socket information. The above bug means the size of struct mytcp exceeds the limit of kernel's predefined per-socket struct size. Provided the struct mytcp cannot be trimmed down any more, and meanwhile ICSK_CA_PRIV_SIZE can not be increased, is there any way to add more info to a socket ? I am thinking about making a certain filed of the struct mytcp be a pointer, so that when the socket gets created, a hook function is invoked to kmalloc some memory to store extra information. And when the socket is destroyed, that memory is also destroyed by some hook function. But this idea seems a little bit messy, and I dunno what the exact hook functions are. Any other remedies? Best,