[llvm] [CI] Try lowering max parallel link jobs on Windows (PR #185255)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/185255

It looks like #177477 might be caused by OOMs due to running too many link jobs at the same time in rare circumstances. It doesn't reproduce often enough for me to be able to easily check the event logs to confirm the OOM killer was involved (I did try 192 runs), but it doesn't hurt to try. This could slightly decrease performance, but given these are vCPUs, even if we need to run only link jobs, we should take only a 10-20% performance hit for the link phase, which is generally not a large portion of the build.

>From f3d867dda3f0ea97e97741e80d9b6701fde4d588 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Sun, 8 Mar 2026 06:41:11 +0000
Subject: [PATCH] [CI] Try lowering max parallel link jobs on Windows

It looks like #177477 might be caused by OOMs due to running too many
link jobs at the same time in rare circumstances. It doesn't reproduce
often enough for me to be able to easily check the event logs to confirm
the OOM killer was involved (I did try 192 runs), but it doesn't hurt to
try. This could slightly decrease performance, but given these are
vCPUs, even if we need to run only link jobs, we should take only a
10-20% performance hit for the link phase, which is generally not a
large portion of the build.
---
 .ci/monolithic-windows.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index 8bda9188c03dc..a04c1ff6e41e6 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -48,7 +48,8 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
       -D CMAKE_EXE_LINKER_FLAGS="/MANIFEST:NO" \
       -D CMAKE_MODULE_LINKER_FLAGS="/MANIFEST:NO" \
       -D CMAKE_SHARED_LINKER_FLAGS="/MANIFEST:NO" \
-      -D LLVM_ENABLE_RUNTIMES="${runtimes}"
+      -D LLVM_ENABLE_RUNTIMES="${runtimes}" \
+      -D LLVM_PARALLEL_LINK_JOBS=16
 
 start-group "ninja"