On Fri, Jun 9, 2023 at 10:28 AM Abel Wu <wuyun.abel@xxxxxxxxxxxxx> wrote: > > This is just a PoC patch intended to resume the discussion about > tcpmem isolation opened by Google in LPC'22 [1]. > > We are facing the same problem that the global shared threshold can > cause isolation issues. Low priority jobs can hog TCP memory and > adversely impact higher priority jobs. What's worse is that these > low priority jobs usually have smaller cpu weights leading to poor > ability to consume rx data. > > To tackle this problem, an interface for non-root cgroup memory > controller named 'socket.urgent' is proposed. It determines whether > the sockets of this cgroup and its descendants can escape from the > constrains or not under global socket memory pressure. > > The 'urgent' semantics will not take effect under memcg pressure in > order to protect against worse memstalls, thus will be the same as > before without this patch. > > This proposal doesn't remove protocal's threshold as we found it > useful in restraining memory defragment. As aforementioned the low > priority jobs can hog lots of memory, which is unreclaimable and > unmovable, for some time due to small cpu weight. > > So in practice we allow high priority jobs with net-memcg accounting > enabled to escape the global constrains if the net-memcg itselt is > not under pressure. While for lower priority jobs, the budget will > be tightened as the memory usage of 'urgent' jobs increases. In this > way we can finally achieve: > > - Important jobs won't be priority inversed by the background > jobs in terms of socket memory pressure/limit. > > - Global constrains are still effective, but only on non-urgent > jobs, useful for admins on policy decision on defrag. > > Comments/Ideas are welcomed, thanks! > This seems to go in a complete opposite direction than memcg promises. Can we fix memcg, so that : Each group can use the memory it was provisioned (this includes TCP buffers) Global tcp_memory can disappear (set tcp_mem to infinity)
