[Peaker]

By "expose it to the application", I mean in the flow-control sense. That send() (or select/epoll/etc) will block until there is room in the TCP window, rather than in the pre-determined buffer which will always be too small or too big.

The way it works now, the kernel is basically forcing applications to have buffer-bloat (fill a 0.5MB socket buffer), or auto-detect RTT or manually select a proper buffer size. All are bad options.

Also, in high-latency-high-bandwidth situations, the default 0.5MB buffer will simply fail to make use of the available bandwidth, so increasing the buffer size does not defeat the purpose. Latency spikes are a different situation, there are cases of constant high latency (e.g: inter-continental 1Gbps links).