netdev - Re: [PATCH net-next v2] unix: add read side socket memory accounting for dgram sockets

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Message-Id: <20140226.145559.1040609936875578841.davem@davemloft.net>
Date:	Wed, 26 Feb 2014 14:55:59 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, yannick@...hler.name,
	eric.dumazet@...il.com, xiyou.wangcong@...il.com, dan@...dstab.net
Subject: Re: [PATCH net-next v2] unix: add read side socket memory
 accounting for dgram sockets

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Wed, 19 Feb 2014 21:08:11 +0100

> On Wed, Feb 19, 2014 at 02:49:27PM -0500, David Miller wrote:
>> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
>> Date: Mon, 17 Feb 2014 14:03:53 +0100
>> 
>> > We still allocate dgram packets with sock_alloc_send_pskb, which now
>> > does normally not block if the socket has too many packets in flight.
>> 
>> It seems like it does to me, it does sock_wait_for_wmem(), right?
> 
> We still do the sock_wait_for_wmem in sock_alloc_send_pskb, correct,
> but we rarly block there, maybe in highly concurrent cases with big
> payloads where one process got interrupted to account the memory to the
> receiving socket.
> 
>> Or are you trying to say that usually this is not the point at which
>> we block, but rather it's when we check the peer's receive queue?
> 
> Exactly.

So my only major objection is that we're now going to incur two atomics
on every single datagram UNIX packet sent between two peers.

I think you can safely put the 'other' sock pointer into the control
block.  Because when we disassociate from a peer any pending packets
in flight to him will be consumed/dropped, so there can't be any
lingering references, right?
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