On 25/05/2022 11:34, Hans Schultz wrote: > On ons, maj 25, 2022 at 11:06, Nikolay Aleksandrov <razor@xxxxxxxxxxxxx> wrote: >> On 24/05/2022 19:21, Hans Schultz wrote: >>>> >>>> Hi Hans, >>>> So this approach has a fundamental problem, f->dst is changed without any synchronization >>>> you cannot rely on it and thus you cannot account for these entries properly. We must be very >>>> careful if we try to add any new synchronization not to affect performance as well. >>>> More below... >>>> >>>>> @@ -319,6 +326,9 @@ static void fdb_delete(struct net_bridge *br, struct net_bridge_fdb_entry *f, >>>>> if (test_bit(BR_FDB_STATIC, &f->flags)) >>>>> fdb_del_hw_addr(br, f->key.addr.addr); >>>>> >>>>> + if (test_bit(BR_FDB_ENTRY_LOCKED, &f->flags) && !test_bit(BR_FDB_OFFLOADED, &f->flags)) >>>>> + atomic_dec(&f->dst->locked_entry_cnt); >>>> >>>> Sorry but you cannot do this for multiple reasons: >>>> - f->dst can be NULL >>>> - f->dst changes without any synchronization >>>> - there is no synchronization between fdb's flags and its ->dst >>>> >>>> Cheers, >>>> Nik >>> >>> Hi Nik, >>> >>> if a port is decoupled from the bridge, the locked entries would of >>> course be invalid, so maybe if adding and removing a port is accounted >>> for wrt locked entries and the count of locked entries, would that not >>> work? >>> >>> Best, >>> Hans >> >> Hi Hans, >> Unfortunately you need the correct amount of locked entries per-port if you want >> to limit their number per-port, instead of globally. So you need a >> consistent > > Hi Nik, > the used dst is a port structure, so it is per-port and not globally. > > Best, > Hans > Yeah, I know. :) That's why I wrote it, if the limit is not a feature requirement I'd suggest dropping it altogether, it can be enforced externally (e.g. from user-space) if needed. By the way just fyi net-next is closed right now due to merge window. And one more thing please include a short log of changes between versions when you send a new one. I had to go look for v2 to find out what changed. >> fdb view with all its attributes when changing its dst in this case, which would >> require new locking because you have multiple dependent struct fields and it will >> kill roaming/learning scalability. I don't think this use case is worth the complexity it >> will bring, so I'd suggest an alternative - you can monitor the number of locked entries >> per-port from a user-space agent and disable port learning or some similar solution that >> doesn't require any complex kernel changes. Is the limit a requirement to add the feature? >> >> I have an idea how to do it and to minimize the performance hit if it really is needed >> but it'll add a lot of complexity which I'd like to avoid if possible. >> >> Cheers, >> Nik
