Merge branch 'metrics_restructure'
This patch series works towards the goal of minimizing the amount of things that can change in an ipv4 route. In a regime where the routing cache is removed, route changes will lead to cloning in the FIB tables or similar. The largest trigger of route metrics writes, TCP, now has it's own cache of dynamic metric state. The timewait timestamps are stored there now as well. As a result of that, pre-cowing metrics is no longer necessary, and therefore FLOWI_FLAG_PRECOW_METRICS is removed. Redirect and PMTU handling is moved back into the ipv4 routes. I'm sorry for all the headaches trying to do this in the inetpeer has caused, it was the wrong approach for sure. Since metrics become read-only for ipv4 we no longer need the inetpeer hung off of the ipv4 routes either. So those disappear too. Also, timewait sockets no longer need to hold onto an inetpeer either. After this series, we still have some details to resolve wrt. PMTU and redirects for a route-cache-less system: 1) With just the plain route cache removal, PMTU will continue to work mostly fine. This is because of how the local route users call down into the PMTU update code with the route they already hold. However, if we wish to cache pre-computed routes in fib_info nexthops (which we want for performance), then we need to add route cloning for PMTU events. 2) Redirects require more work. First, redirects must be changed to be handled like PMTU. Wherein we call down into the sockets and other entities, and then they call back into the routing code with the route they were using. So we'll be adding an ->update_nexthop() method alongside ->update_pmtu(). And then, like for PMTU, we'll need cloning support once we start caching routes in the fib_info nexthops. But that's it, we can completely pull the trigger and remove the routing cache with minimal disruptions. As it is, this patch series alone helps a lot of things. For one, routing cache entry creation should be a lot faster, because we no longer do inetpeer lookups (even to check if an entry exists). This patch series also opens the door for non-DST_HOST ipv4 routes, because nothing fundamentally cares about rt->rt_dst any more. It can be removed with the base routing cache removal patch. In fact, that was the primary goal of this patch series. Signed-off-by: David S. Miller <email@example.com>
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