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bbaa7aef7b
Previously, congestion window was increased any time each time a new acknowledge was received. However, it did not take into account the window filling level. In a network condition with negligible loss, this will cause the window to be incremented until the maximum value (by default 480k), even though the application does not have enough data to fill it. In most cases, this issue is not noticeable. However, it may lead to excessive memory consumption when a QUIC connection is suddendly interrupted, as in this case haproxy will fill the window with retransmission. It even has caused OOM crash when thousands of clients were interrupted at once on a local network benchmark. Fix this by first checking window level prior to every incrementation via a new helper function quic_cwnd_may_increase(). It was arbitrarily decided that the window must be at least 50% full when the ACK is handled prior to increment it. This value is a good compromise to keep window in check while still allowing fast increment when needed. Note that this patch only concerns cubic and newreno algorithm. BBR has already its notion of application limited which ensures the window is only incremented when necessary. This should be backported up to 2.6.