nfsd: handle drc over-allocation gracefully.

	unsigned long avail, total_avail;

	spin_lock(&nfsd_drc_lock);

	if (nfsd_drc_max_mem > nfsd_drc_mem_used)

		total_avail = nfsd_drc_max_mem - nfsd_drc_mem_used;

	else

		/* We have handed out more space than we chose in

		 * set_max_drc() to allow.  That isn't really a

		 * problem as long as that doesn't make us think we

		 * have lots more due to integer overflow.

		 */

		total_avail = 0;

	avail = min((unsigned long)NFSD_MAX_MEM_PER_SESSION, total_avail);

	/*

	 * Never use more than a third of the remaining memory,

	 * unless it's the only way to give this client a slot:

	 * unless it's the only way to give this client a slot.

	 * Give the client one slot even if that would require

	 * over-allocation--it is better than failure.

	 */

	avail = clamp_t(unsigned long, avail, slotsize, total_avail/3);

	num = min_t(int, num, avail / slotsize);

	num = max_t(int, num, 1);

	nfsd_drc_mem_used += num * slotsize;

	spin_unlock(&nfsd_drc_lock);

	 * performance.  When short on memory we therefore prefer to

	 * decrease number of slots instead of their size.  Clients that

	 * request larger slots than they need will get poor results:

	 * Note that we always allow at least one slot, because our

	 * accounting is soft and provides no guarantees either way.

	 */

	ca->maxreqs = nfsd4_get_drc_mem(ca);

	if (!ca->maxreqs)

		return nfserr_jukebox;

	return nfs_ok;

}