> On Aug 27, 2015, at 4:47 PM, Vlad Yasevich <vyasevic@xxxxxxxxxx> wrote: > > On 08/27/2015 05:02 PM, Nikolay Aleksandrov wrote: >> >>> On Aug 26, 2015, at 9:57 PM, roopa <roopa@xxxxxxxxxxxxxxxxxxx> wrote: >>> >>> On 8/26/15, 4:33 AM, Nikolay Aleksandrov wrote: >>>>> On Aug 25, 2015, at 11:06 PM, David Miller <davem@xxxxxxxxxxxxx> wrote: >>>>> >>>>> From: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx> >>>>> Date: Tue, 25 Aug 2015 22:28:16 -0700 >>>>> >>>>>> Certainly, that should be done and I will look into it, but the >>>>>> essence of this patch is a bit different. The problem here is not >>>>>> the size of the fdb entries, it’s more the number of them - having >>>>>> 96000 entries (even if they were 1 byte ones) is just way too much >>>>>> especially when the fdb hash size is small and static. We could work >>>>>> on making it dynamic though, but still these type of local entries >>>>>> per vlan per port can easily be avoided with this option. >>>>> 96000 bits can be stored in 12k. Get where I'm going with this? >>>>> >>>>> Look at the problem sideways. >>>> Oh okay, I misunderstood your previous comment. I’ll look into that. >>>> >>> I just wanted to add the other problems we have had with keeping these macs (mostly from userspace POV): >>> - add/del netlink notification storms >>> - and large netlink dumps >>> >>> In addition to in-kernel optimizations, will be nice to have a solution that reduces the burden on userspace. That will need a newer netlink dump format for fdbs. Considering all the changes needed, Nikolays patch seems less intrusive. >> >> Right, we need to take these into account as well. I’ll continue the discussion on this (or restart it) because >> I looked into using a bitmap for the local entries only and while it fixes the scalability issue, it presents >> a few new ones which are mostly related to the fact that these entries now exist only without a vlan >> and if a new mac comes along which matches one of these but is in a vlan, the entry will get created >> in br_fdb_update() unless we add a second lookup, but that will slow down the learning path. >> Also this change requires an update of every fdb function that uses the vid as a key (every fdb function?!) >> because now we can have the mac in two places instead of one which is a pretty big churn with lots >> of conditionals all over the place and I don’t like it. Adding this complexity for the local addresses only >> seems like an overkill, so I think to drop this issue for now. > > I seem to recall Roopa and I and maybe a few others have discussing this a few > years ago at plumbers, I can't remember the details any more. All these local > addresses add a ton of confusion. Does anyone (Stephen?) remember what the > original reason was for all these local addresses? I wonder if we can have > a nob to disable all of them (not just per vlan)? That might be cleaner and > easier to swallow. > Right, this would be the easiest way and if the others agree - I’ll post a patch for it so we can have some way to resolve it today and even if we fix the scalability issue, this is still a valid case that some people don’t want local fdbs installed automatically. Any objections to this ? >> This patch (that works around the initial problem) also has these issues. >> Note that one way to take care of this in a more straight-forward way would be to have each entry >> with some sort of a bitmap (like Vlad has tried earlier) and then we can combine the paths so most >> of these issues disappear, but that will not be easy as was already commented earlier. I’ve looked >> briefly into doing this with rhashtable so we can keep the memory footprint for each entry relatively >> small but it still affects the performance and we can have thousands of resizes happening. >> > > So, one of the earlier approaches that I've tried (before rhashtable was > in the kernel) was to have a hash of vlan ids each with a data structure > pointing to a list of ports for a given vlan as well as a list of fdbs for > a given vlan. As far as scalability goes, that's really the best approach. > It would also allow us to do packet accounting per vlan. The only concern > at the time was performance of ingress lookup. I think rhashtables might > help with this as well as ability to grow the footprint of the vlan hash > table dynamically. > > -vlad > I’ll look into it but I’m guessing the learning will become a more complicated process with additional allocations and some hash handling. >> On the notification side if we can fix that, we can actually delete the 96000 entries without creating a >> huge notification storm and do a user-land workaround of the original issue, so I’ll look into that next. >> >> Any comments or ideas are very welcome. >> >> Thank you, >> Nik
