On Sat, Aug 27, 2016 at 9:25 AM, Eric Dumazet <eric.duma...@gmail.com> wrote: > > On Sat, 2016-08-27 at 09:13 -0700, Yuchung Cheng wrote: > > On Sat, Aug 27, 2016 at 7:37 AM, Eric Dumazet <eric.duma...@gmail.com> > > wrote: > > > > > > > + /* Only socket owner can try to collapse/prune rx queues > > > + * to reduce memory overhead, so add a little headroom here. > > > + * Few sockets backlog are possibly concurrently non empty. > > > + */ > > > + limit += 64*1024; > > Just a thought: only add the headroom if ofo queue exists (e.g., signs > > of losses ore recovery). > > Testing the ofo would add a cache line miss, and likely slow down the > other cpu processing the other packets for this flow. > > Also, even if the ofo does not exist, the sk_rcvbuf budget can be > consumed by regular receive queue. > > We still need to be able to process incoming ACK, if both send and > receive queues are 'full'. > > > > > btw is the added headroom subject to the memory pressure check? > > Remind that the backlog check here is mostly to avoid some kind of DOS > attacks that we had in the past. > > While we should definitely prevents DOS attacks, we should also not drop > legitimate traffic. > > Here, number of backlogged sockets is limited by the number of cpus in > the host (if CONFIG_PREEMPT is disabled), or number of threads blocked > during a sendmsg()/recvmsg() (if CONFIG_PREEMPT is enabled) > > So we do not need to be ultra precise, just have a safe guard. > > The pressure check will be done at the time skbs will be added into a > receive/ofo queue in the very near future. Good to know. Thanks.
> > > Thanks ! > > >
