[RFC] per-containers tcp buffer limitation
glommer at parallels.com
Wed Aug 24 15:54:47 PDT 2011
This is a proof of concept of some code I have here to limit tcp send
and receive buffers per-container (in our case). At this phase, I am
more concerned in discussing my approach, so please curse my family no
further than the 3rd generation.
The problem we're trying to attack here, is that buffers can grow and
fill non-reclaimable kernel memory. When doing containers, we can't
afford having a malicious container pinning kernel memory at will,
therefore exhausting all the others.
So here a container will be seen in the host system as a group of tasks,
grouped in a cgroup. This cgroup will have files allowing us to specify
global per-cgroup limits on buffers. For that purpose, I created a new
sockets cgroup - didn't really think any other one of the existing would
As for the network code per-se, I tried to keep the same code that deals
with memory schedule as a basis and make it per-cgroup.
You will notice that struct proto now take function pointers to values
controlling memory pressure and will return per-cgroup data instead of
global ones. So the current behavior is maintained: after the first
threshold is hit, we enter memory pressure. After that, allocations are
Only tcp code was really touched here. udp had the pointers filled, but
we're not really controlling anything. But the fact that this lives in
generic code, makes it easier to do the same for other protocols in the
For this patch specifically, I am not touching - just provisioning -
rmem and wmem specific knobs. I should also #ifdef a lot of this, but
hey, remember: rfc...
One drawback of this approach I found, is that cgroups does not really
work well with modules. A lot of the network code is modularized, so
this would have to be fixed somehow.
Let me know what you think.
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