A benchmark with go1.16 on amd64 resulted in an overall maximum memory
usage of 15GiB. This means we now lower the `KUBE_PARALLEL_BUILD_MEMORY`
to `20` to still have some room left.
The benchmark has been done with the following `Dockerfile`:
```dockerfile
FROM k8s.gcr.io/build-image/kube-cross:v1.16.0-1
RUN apt-get update && apt-get install -y time
WORKDIR /go/src/k8s.io/kubernetes
RUN git clone https://github.com/kubernetes/kubernetes
ENV KUBE_PARALLEL_BUILD_MEMORY=0
RUN /usr/bin/time -v make -C kubernetes cross-in-a-container
```
The value of interest from the output:
```
Maximum resident set size (kbytes): 1847108
```
The RSS is not the only value we have to consider. During the runtime I
measured the usage of the cached memory, which gets peaks up to 15GiB.
Test machine specs:
- CPU: 2 x Intel Scalable Gold 5120 28-Core Processor @ 2.2GHz
- RAM: 384GB
- Disk: 1 x 3.8TB NVME
- OS: Debian 10 (buster)
Signed-off-by: Sascha Grunert <sgrunert@redhat.com>
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