Hello.
In 2.6.10 there has been a "bug" introduced. You may also call it a feature, but its a crappy
feature for big servers. It seems the kernel is dynamically adjusting the buffer-space available for
sockets. Even if send-buffer has been set to 1024 KB, the kernel blocks at less if there are enough
sockets in use. If you have 10 sockets with 1024 KB each, they do not block at all, using full 1024
KB. If you have 4000 sockets, they only use 200 KB. So it seems its blocking at 800 MB. This is
good, if you have a 1/3 system, because else the kernel would run out of low mem. But I have a 2/2
system and I need them for buffers. So what can I do? Where can I adjust the "pool"?
You can set the upper bound by setting tcp_wmem. There are three values
all documented in Documentation/networking/ip-sysctl.txt
This feature is meant also to prevent remote denial of service
attacks. It limits the amount of system memory TCP can
consume on your system.
Before this feature went in, it's really easy to remotely make a system
consume %90 of system memory just with socket buffers.
Thank you for your reply.
Yes this is possible for most situations. Isn't there a way to disable it or at least adjust the
level? As said, I have a 2/2 system and I would like to set it to 1500 MB. this is important for my
big server.
Oh and for that DOS-thingy, my two cents: It would be better if buffer-sockets are dynamically
adjusted. So that memory is only allocated if the queue is really needed. Most of the allocated
memory is mostly unused because queues are mostly empty.
Please help me.
Thank you in advance,
Chris
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