Off List Message - Kernel Problem - Respond To Me

Hello-
The City of Largo is a big KDE/Linux shop, as many of you are
aware we run
about 800 unique users, on 450 thin clients running the KDE desktop.

We upgraded from RedHat 7.2 to RedHat 7.3 and therefore from KDE
2.x to
KDE 3.x. There seems to be a scaling problem that was introduced in KDE 3.x that we cannot resolve. Previously a Dual 933Mhz system would easily run 200+ users at once, but now the KDE 3.x runs out of resources around 91 users. We have been told that it's related to the maximum number of threads allowed in the 2.4 kernel itself and is not something that can be fixed. When we get to the 91st person, we started getting this message-->

Nov 19 14:09:41 desktop_a kernel: ldt allocation failed

We get this error over and over again and no additional users can log into the server.

I'm not on the linux-kernel list, but if anyone has insight into this issue, please drop me a line. If you know a way to fix this in the 2.4 kernel too, or can verify that we have to wait for 2.5/2.6 we need to know that too.

Thanks as always for your help
Dave Richards
City of Largo, FL
Systems Administrator.

Dave Richards <[email protected]>

IIRC this has been hit in threaded benchmarks before; ISTR a fix for LDT OOM going around, probably manfred's stuff which is in 2.5 and 2.4-ac.

Thanks,
Bill

Correct, the patch is in 2.4-ac, and I'll send it to Marcelo for 2.4.21.

How many concurrent processes are running? Each thread that is linked against libpthread consumes 64 kB vmalloc space, and on SMP you have around 96 MB vmalloc space. I'd expect OOM at 1500 threads.

With the fix applied, no vmalloc space is needed for libpthread. --
Manfred

You can do a dirty hack workaround by increasing VMALLOC_RESERVE as well, I've done that in the past ...

M.