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

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Message-ID: <87hbf9uncz.fsf@basil.nowhere.org>
Date:	Mon, 22 Nov 2010 21:14:52 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Alban Crequy <alban.crequy@...labora.co.uk>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay.sievers@...y.org>,
	Ian Molton <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

Alban Crequy <alban.crequy@...labora.co.uk> writes:

>+static DEFINE_SPINLOCK(unix_multicast_lock);

For DBUS it's probably ok, but I suspect for other usages
the global lock in the multipath fast path is going to hurt
sooner or later.

> +
> +        /* Allocate for the set and hope the number of recipients does not
> +	 * change while the lock is released. If it changes, we have to try
> +	 * again... We allocate a bit more than needed, so if a _few_ members
> +	 * are added in a multicast group meanwhile, we don't always need to
> +	 * try again. */
> +	recipient_cnt += 5;
> +
> +	set = kmalloc(sizeof(struct sock_set)
> +		      + sizeof(struct sock_item) * recipient_cnt,
> +	    GFP_KERNEL);

FWIW for a large number of sockets this will likely run into
memory fragmentation issues. There are various workarounds like
fallback to vmalloc or use something like flex_arrays.


-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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