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07db945b09
There is a relation between the maximum number of vCPUs and the
memory footprint, if QEMU maxcpus option and kernel nr_cpus
cmdline argument are big, then memory footprint is big, this
issue only occurs if CPU hotplug support is enabled in the kernel,
might be because of kernel needs to allocate resources to watch all
sockets waiting for a CPU to be connected (ACPI event).
For example
```
+---------------+-------------------------+
| | Memory Footprint (KB) |
+---------------+-------------------------+
| NR_CPUS=240 | 186501 |
+---------------+-------------------------+
| NR_CPUS=8 | 110684 |
+---------------+-------------------------+
```
In order to do not affect CPU hotplug and allow to users to have containers
with the same number of physical CPUs, this patch tries to mitigate the
big memory footprint by using the actual number of physical CPUs as the
maximum number of vCPUs for each container if `default_maxvcpus` is <= 0 in
the runtime configuration file, otherwise `default_maxvcpus` is used as the
maximum number of vCPUs.
Before this patch a container with 256MB of RAM
```
total used free shared buff/cache available
Mem: 195M 40M 113M 26M 41M 112M
Swap: 0B 0B 0B
```
With this patch
```
total used free shared buff/cache available
Mem: 236M 11M 188M 26M 36M 186M
Swap: 0B 0B 0B
```
fixes #295
Signed-off-by: Julio Montes <julio.montes@intel.com>