netdev - Re: [PATCH net-next] tcp: refine tcp_prune_ofo

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Message-Id: <20160818.233643.732250691565806768.davem@davemloft.net>
Date:   Thu, 18 Aug 2016 23:36:43 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org, soheil@...gle.com, ncardwell@...gle.com,
        ycheng@...gle.com, csg@...gle.com, vanj@...gle.com
Subject: Re: [PATCH net-next] tcp: refine tcp_prune_ofo_queue() to not drop
 all packets

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 17 Aug 2016 14:17:09 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Over the years, TCP BDP has increased a lot, and is typically
> in the order of ~10 Mbytes with help of clever Congestion Control
> modules.
> 
> In presence of packet losses, TCP stores incoming packets into an out of
> order queue, and number of skbs sitting there waiting for the missing
> packets to be received can match the BDP (~10 Mbytes)
> 
> In some cases, TCP needs to make room for incoming skbs, and current
> strategy can simply remove all skbs in the out of order queue as a last
> resort, incurring a huge penalty, both for receiver and sender.
> 
> Unfortunately these 'last resort events' are quite frequent, forcing
> sender to send all packets again, stalling the flow and wasting a lot of
> resources.
> 
> This patch cleans only a part of the out of order queue in order
> to meet the memory constraints.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Looks great, applied.