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

Alban Crequy [off-list ref] 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.