kernel-build: make workspace tmpfs on codebuild runners

AWS CodeBuild runners have lots of mostly unused memory. And the
kernel build jobs do quite a bit of disk writes, which are never
actually read. This unnecessarily slows down the execution.

When running on CodeBuild, before executing the build, make sure
GITHUB_WORKSPACE directory is a tmpfs filesystem, to make use of
available memory and avoid unnecessary IO operations.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

Author: theihor

.github/scripts/tmpfsify-workspace.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+set -x -euo pipefail
+
+TMPFS_SIZE=20 # GB
+MEM_TOTAL=$(awk '/MemTotal/ {print int($2/1024)}' /proc/meminfo)
+
+# sanity check: total mem is at least double TMPFS_SIZE
+if [ $MEM_TOTAL -lt $(($TMPFS_SIZE*1024*2)) ]; then
+    echo "tmpfsify-workspace.sh: will not allocate tmpfs, total memory is too low (${MEM_TOTAL}MB)"
+    exit 0
+fi
+
+dir="$(basename "$GITHUB_WORKSPACE")"
+cd "$(dirname "$GITHUB_WORKSPACE")"
+mv "${dir}" "${dir}.backup"
+mkdir "${dir}"
+sudo mount -t tmpfs -o size=${TMPFS_SIZE}G tmpfs "${dir}"
+rsync -a "${dir}.backup/" "${dir}"
+cd -
+

.github/workflows/kernel-build.yml

@@ -66,6 +66,11 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: ${{ inputs.download_sources && 1 || env.BPF_NEXT_FETCH_DEPTH }}
+
+      - if: ${{ env.RUNNER_TYPE == 'codebuild' }}
+        shell: bash
+        run: .github/scripts/tmpfsify-workspace.sh
+
       - if: ${{ inputs.download_sources }}
         name: Download bpf-next tree
         env: