Re: [PATCH net-next] tcp: prepare skbs for better sack shifting

From: Eric Dumazet <redacted>
Date: Thu, 15 Sep 2016 09:33:02 -0700

From: Eric Dumazet <redacted>

With large BDP TCP flows and lossy networks, it is very important
to keep a low number of skbs in the write queue.

RACK and SACK processing can perform a linear scan of it.

We should avoid putting any payload in skb->head, so that SACK
shifting can be done if needed.

With this patch, we allow to pack ~0.5 MB per skb instead of
the 64KB initially cooked at tcp_sendmsg() time.

This gives a reduction of number of skbs in write queue by eight.
tcp_rack_detect_loss() likes this.

We still allow payload in skb->head for first skb put in the queue,
to not impact RPC workloads.

Signed-off-by: Eric Dumazet <redacted>
Cc: Yuchung Cheng <redacted>

Applied.