The background is that I’m running video capture operations in an LXC container and have behaviour reminiscent of memory limitation issues. The host system is Debian Jessie with its packaged 1.0.6 LXC. I have plenty of memory on the host and sensible (I think) shared memory settings:
# free total used free shared buffers cached Mem: 24701384 7938664 16762720 188480 2737872 608968 # sysctl -a | grep -E "shmall|shmmax" kernel.shmall = 655360 kernel.shmmax = 2500000000
I was aware that I might have issues setting the container up to use this, but what I found when I interrogated it was this:
# sysctl -a | grep -E "shmall|shmmax" kernel.shmall = 18446744073692774399 kernel.shmmax = 18446744073692774399
Now, by my reckoning that’s more than the physical memory actually in the host system. There are not shmall/shmmax settings in the container’s sysctl.conf.
So, what’s going on? Does the container actually have pretty much unlimited shared memory access within the constraints of the host system’s physical RAM, are those numbers bogus (in which case what should I be looking at) or am I mis-reading something? How do I find out what the effective values for shmall and shmmax in the container actually are?
The system in question is mission critical and delicate in many ways so I’d rather stick to Jessie and the stock Debian packages if possible although I know there are more recent LXC versions out there. However, if this is a known issue which has been resolved, that would be useful to know.
With thanks in advance,