From a3d3049825875d0d8c197cf4a36d230ff5d49371 Mon Sep 17 00:00:00 2001
From: Michael Heller <21163552+mdheller@users.noreply.github.com>
Date: Thu, 23 Jul 2026 09:22:33 -0400
Subject: [PATCH] windows: add 14G swap + MOZ_BUILD_JOBS=3 on CI to survive
 rustc OOM (exit 143)

-j$(nproc)=4 still OOM-killed the neqo/mls-platform-api/icu rustc cluster on
16GB runners (each of those is multi-GB; exit 143 = cargo propagating an
OOM-killed child). Add a 14G swapfile to absorb the spikes and expose
MOZ_BUILD_JOBS so CI can run -j3 while the 32-core sovereign builder keeps
its nproc default.
---
 .github/workflows/nightly-windows.yml | 12 ++++++++++++
 scripts/build-windows-cross.sh        |  9 +++++----
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/nightly-windows.yml b/.github/workflows/nightly-windows.yml
index e473c37..6c13c91 100644
--- a/.github/workflows/nightly-windows.yml
+++ b/.github/workflows/nightly-windows.yml
@@ -30,6 +30,8 @@ jobs:
       VERSION: 150.0.1
       RELEASE: 1
       PROFILE: human-secure
+      # 16GB runners OOM the neqo/mls/icu rustc cluster at higher parallelism.
+      MOZ_BUILD_JOBS: 3
 
     steps:
       - name: Checkout
@@ -41,6 +43,16 @@ jobs:
             /opt/hostedtoolcache/CodeQL /usr/local/share/boost "$AGENT_TOOLSDIRECTORY" || true
           df -h /
 
+      - name: Add swap (absorb rustc memory spikes on 16GB runners)
+        run: |
+          sudo swapoff -a || true
+          sudo rm -f /mnt/swapfile /swapfile || true
+          sudo fallocate -l 14G /mnt/swapfile
+          sudo chmod 600 /mnt/swapfile
+          sudo mkswap /mnt/swapfile
+          sudo swapon /mnt/swapfile
+          free -h
+
       - name: Cache Mozilla toolchain (clang-cl, cbindgen)
         uses: actions/cache@v4
         with:
diff --git a/scripts/build-windows-cross.sh b/scripts/build-windows-cross.sh
index 5df56ea..f23b283 100755
--- a/scripts/build-windows-cross.sh
+++ b/scripts/build-windows-cross.sh
@@ -157,10 +157,11 @@ export PATH="$MOZ_CLANG_BIN:$HOME/.cargo/bin:$PATH"
 ulimit -n "$NOFILE"
 
 ./mach configure
-# Cap parallelism at the core count: mach's memory heuristic over-parallelizes
-# on 16GB CI runners and a burst of rustc processes gets the job SIGTERM'd
-# (exit 143, ~10min in). -j$(nproc) is also correct on the big sovereign builder.
-./mach build -j"$(nproc)"
+# Cap parallelism: mach's memory heuristic over-parallelizes on 16GB CI runners
+# and a burst of multi-GB rustc processes (neqo/mls/icu) gets OOM-killed (exit
+# 143, ~10min in). MOZ_BUILD_JOBS lets CI dial it down (the workflow sets a low
+# value + adds swap); defaults to nproc for the 32-core sovereign builder.
+./mach build -j"${MOZ_BUILD_JOBS:-$(nproc)}"
 ./mach package
 
 log "artifacts"