Print a (rate-limited) warning when UMA zone is full.

[Alfred Perlstein]

On 11/29/12 1:01 AM, Pawel Jakub Dawidek wrote:
> Hi.
>
> I'd like to propose the following patch:
>
> 	http://people.freebsd.org/~pjd/patches/uma_warning.patch
>
> When UMA zone is created, one can add configure a warning that should be
> printed when UMA zone is full by calling:
>
> 	uma_zone_set_warning(socket_zone,
> 	    "kern.ipc.maxsockets limit exceeded, please see tuning(7).");
>
> It was very easy to find and fix the problem when I saw messages on the
> console that kern.maxfiles limit is reached, but when I hit
> kern.ipc.maxsockets limit and started to get ENOBUFS errors it took me a
> while to figure out what to tune.
>
> This patch allows to configure advice for the use and give him some
> details in a very easy way. The warning printed on the console is
> rate-limited to one per second.
>
This is great.

Please commit this as soon as you can.  An MFC would be awesome.

-Alfred