From: "Lachlan Andrew" <redacted>
Date: Tue, 8 Jan 2008 17:34:03 -0800

John also suggested freeing the packets as a lower priority task, just
doing it after they're acknowledged.

When the ACK finally comes, you could do something like moving John's
entire list of packets to a "to be freed" list, and free a few every
time (say) another ACK comes in.

You could, but this requires extra state and the operations to
properly queue such items to the deferred task and wake it up.

And none of this would be necessary if we could make SACK
indications hard.