Messages in this thread | | | From | Eric Dumazet <> | Date | Sat, 28 Jul 2018 09:28:52 -0700 | Subject | Re: [PATCH net-next 1/2] tcp: call tcp_drop() in tcp collapse |
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On Sat, Jul 28, 2018 at 12:43 AM Yafang Shao <laoar.shao@gmail.com> wrote: > > On Sat, Jul 28, 2018 at 11:38 AM, Eric Dumazet <edumazet@google.com> wrote: > > On Fri, Jul 27, 2018 at 8:35 PM Yafang Shao <laoar.shao@gmail.com> wrote: > > > >> So what about LINUX_MIB_TCPOFOMERGE ? > >> Regarding LINUX_MIB_TCPOFOMERGE, a skb is already covered by another > >> skb, is that dropping the packet or simply lowering the memory > >> overhead ? > > > > What do you think ? > > > > If you receive two times the same payload, don't you have to drop one > > of the duplicate ? > > > > There is a a big difference between the two cases. > > If the drop caused some data lost (which may then cause retransmition > or something), then this is a really DROP. > While if the drop won't cause any data lost, meaning it is a > non-harmful behavior, I think it should not be defined as DROP. > This is my suggestion anyway.
Sigh.
We count drops, not because they are ' bad or something went wrong'.
If TCP stack receives twice the same sequence (same payload), we _drop_ one of the duplicate, so we account for this event.
When ' collapsing' we reorganize our own storage, not because we have to drop a payload, but for some memory pressure reason. We have specific SNMP counters to account for these, we do not want to pretend a packet was ' dropped' since it was not.
If we have to _drop_ some packets, it is called Pruning, and we do properly account for these drops.
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