Messages in this thread | | | Subject | Re: [RFC][PATCH 0/9] Network receive deadlock prevention for NBD | From | Peter Zijlstra <> | Date | Sat, 12 Aug 2006 12:18:07 +0200 |
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On Sat, 2006-08-12 at 13:37 +0400, Evgeniy Polyakov wrote: > On Sat, Aug 12, 2006 at 11:19:49AM +0200, Peter Zijlstra (a.p.zijlstra@chello.nl) wrote: > > > As you described above, memory for each packet must be allocated (either > > > from SLAB or from reserve), so network needs special allocator in OOM > > > condition, and that allocator should be separated from SLAB's one which > > > got OOM, so my purpose is just to use that different allocator (with > > > additional features) for netroking always. Since every piece of > > > networking is limited (socket queues, socket numbers, hardware queues, > > > hardware wire speeds an so on) there is always a maximum amount of > > > memory it can consume and can never exceed, so if network allocator will > > > get that amount of memory at the begining, it will never meet OOM, > > > so it will _always_ work and thus can allow to make slow progress for > > > OOM-capable things like block devices and swap issues. > > > There are no special reserve and no need to switch to/from it and > > > no possibility to have OOM by design. > > > > I'm not sure if the network stack is bounded as you say; for instance > > imagine you taking a lot of packets for blocked user-space processes, > > these will just accumulate in the network stack and go nowhere. In that > > case memory usage is very much unbounded. > > No it is not. There are socket queues and they are limited. Things like > TCP behave even better. > > > Even if blocked sockets would only accept a limited amount of packets, > > it would then become a function of the amount of open sockets, which is > > again unbounded. > > Does it? I though it is possible to only have 64k of working sockets per > device in TCP.
65535 sockets * 128 packets * 16384 bytes/packet = 1^16 * 1^7 * 1^14 = 1^(16+7+14) = 1^37 = 128G of memory per IP
And systems with a lot of IP numbers are not unthinkable.
I wonder what kind of system you have to feel that that is not a problem. (I'm not sure on the 128 packets per socket, and the 16k per packet is considering jumbo frames without scather gather receive)
> If system is limited enough to provide enough memory for network tree > allocator, it is possible to create it's own drop condition inside NTA, > but it must be saparated from the weakest chain element in that > conditions - SLAB OOM.
Hence the alternative allocator to use on tight memory conditions.
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