diff --git a/README.md b/README.md
index 55e0c87..04d6668 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ runs-on: [self-hosted, vm]
 - `controller`：接收 Gitea `workflow_job` webhook，将指定 label 的 queued job
   发布到 NATS JetStream。
 - `worker`：领取任务、限制并发，并通过 Pod 或 microVM backend 创建一次性环境。
-- `microvm-runner-launch`：为每个任务复制 flat qcow2 root disk（支持时使用 reflink）、创建 NoCloud seed 和 TAP，运行
+- `microvm-runner-launch`：为每个任务以 direct I/O 转换出 flat qcow2 root disk、创建 NoCloud seed 和 TAP，运行
   Cloud Hypervisor，退出后完整清理。
 - `guest-runner`：在 guest 中领取一次性 runner registration token，注册 ephemeral
   runner，执行一个 job 后关机。
diff --git a/scripts/microvm-runner-launch b/scripts/microvm-runner-launch
index ff3865b..64e3a5c 100755
--- a/scripts/microvm-runner-launch
+++ b/scripts/microvm-runner-launch
@@ -45,8 +45,9 @@ test -r "$base_image"
 test -r "$firmware"
 install -d -m 0700 "$state_root/instances" "$vm_dir"
 # Cloud Hypervisor cannot open qcow2 backing chains.  Keep each disposable
-# root disk flat; reflink-capable storage still makes this copy cheap.
-cp --reflink=auto --sparse=always "$base_image" "$overlay"
+# root disk flat and bypass the LXC page cache: caching both a 5 GiB copy and
+# guest RAM can otherwise trigger the container memory limit.
+qemu-img convert -q -T none -t none -f qcow2 -O qcow2 "$base_image" "$overlay"
 
 cat >"$vm_dir/meta-data" <<EOF
 instance-id: $instance_id