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

[Andi Kleen <andi@firstfloor.org>]

Alban Crequy <alban.crequy@collabora.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@linux.intel.com -- Speaking for myself only.