netdev - Re: [PATCH net-next 1/8] tipc: decrease connection flow control window

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Message-Id: <20140513.000530.154961879638643331.davem@davemloft.net>
Date:	Tue, 13 May 2014 00:05:30 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	jon.maloy@...csson.com
Cc:	netdev@...r.kernel.org, paul.gortmaker@...driver.com,
	erik.hugne@...csson.com, ying.xue@...driver.com, maloy@...jonn.com,
	tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH net-next 1/8] tipc: decrease connection flow control
 window

From: Jon Maloy <jon.maloy@...csson.com>
Date: Fri,  9 May 2014 09:13:22 -0400

> Memory overhead when allocating big buffers for data transfer may
> be quite significant. E.g., truesize of a 64 KB buffer turns out
> to be 132 KB, 2 x the requested size.
> 
> This invalidates the "worst case" calculation we have been
> using to determine the default socket receive buffer limit,
> which is based on the assumption that 1024x64KB = 67MB buffers
> may be queued up on a socket.
> 
> Since TIPC connections cannot survive hitting the buffer limit,
> we have to compensate for this overhead.
> 
> We do that in this commit by dividing the fix connection flow
> control window from 1024 (2*512) messages to 512 (2*256). Since
> older version nodes send out acks at 512 message intervals,
> compatibility with such nodes is guaranteed, although performance
> may be non-optimal in such cases.
> 
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>
> Reviewed-by: Ying Xue <ying.xue@...driver.com>

So all I have to do is open 64 sockets to make TIPC commit to 4GB
of ram at once?

I really think you need to rethink this, the socket limits are
there for a reason.
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