[ovs-dev] why the max action length is 32K in kernel?

[ychen]

in function nla_alloc_flow_actions(), there is a check if action length is greater than MAX_ACTIONS_BUFSIZE(32k), then kernel datapath flow will not be installed, and packets will droppped.
but in function xlate_actions(), there is such clause:
if (nl_attr_oversized(ctx.odp_actions->size)) {
        /* These datapath actions are too big for a Netlink attribute, so we
         * can't hand them to the kernel directly.  dpif_execute() can execute
         * them one by one with help, so just mark the result as SLOW_ACTION to
         * prevent the flow from being installed. */
        COVERAGE_INC(xlate_actions_oversize);
        ctx.xout->slow |= SLOW_ACTION;
    }
and in function nl_attr_oversized(), the clause is like this:
return payload_size > UINT16_MAX - NLA_HDRLEN;


so we can see that in user space, max action length is almost 64K, but in kernel space, max action length is only 32K. 
my question is: why the max action length is different? packet will drop when its action length exceeds 32K, but packet can excute in slow path when its action length exceeds 64K?