netdev - Re: [PATCH 4/9] AF_UNIX: find the recipients for multicast messages

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Date:	Mon, 22 Nov 2010 11:05:19 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	alban.crequy@...labora.co.uk
Cc:	eric.dumazet@...il.com, shemminger@...tta.com, gorcunov@...nvz.org,
	adobriyan@...il.com, lennart@...ttering.net, kay.sievers@...y.org,
	ian.molton@...labora.co.uk, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] AF_UNIX: find the recipients for multicast messages

From: Alban Crequy <alban.crequy@...labora.co.uk>
Date: Mon, 22 Nov 2010 18:36:17 +0000

> unix_find_multicast_recipients() builds an array of recipients. It can either
> find the peers of a specific multicast address, or find all the peers of all
> multicast group the sender is part of.
> 
> Signed-off-by: Alban Crequy <alban.crequy@...labora.co.uk>

You really should use RCU to lock this stuff, this way sends run
lockless and have less worries wrt. the memory allocation.  You'll
also only take a spinlock in the write paths which change the
multicast groups, which ought to be rare.

Although to be honest you should optimize the case of small numbers of
recipients, in the same way we optimize small numbers of iovecs on
sends.  Have an on-stack array that holds a small number of entries
and use that if the set fits, otherwise dynamic allocation.
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