[PATCH 3/3] selftests: mm: add script for memory allocation stall test

[Jason Miu <jasonmiu@google.com>]

Integrate page_alloc_stall.sh, a script to synchronize userspace and
kernelspace workloads to reproduce page allocation stalls.

Provision a synthetic loopback zswap block device, inject the
test_mempress_timer.ko module to generate atomic page allocations
inside kernel timers, and execute the page_alloc_stall_pressure.py
payload to induce system-wide swap activity.

Signed-off-by: Jason Miu <jasonmiu@google.com>
---
 .../testing/selftests/mm/page_alloc_stall.sh  | 80 +++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 tools/testing/selftests/mm/page_alloc_stall.sh

diff --git a/tools/testing/selftests/mm/page_alloc_stall.sh b/tools/testing/selftests/mm/page_alloc_stall.sh
new file mode 100644
index 000000000000..3ece026fd680
--- /dev/null
+++ b/tools/testing/selftests/mm/page_alloc_stall.sh
@@ -0,0 +1,80 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# page_alloc_stall.sh
+#
+# Orchestrator script to generate concurrent userspace and kernelspace
+# memory allocation pressure over a synthetic zswap backing block device
+# to artificially induce systemic memory contention.
+#
+# Dependencies:
+# - External memtoy binary (Source: https://github.com/kosaki/memtoy)
+#
+# Usage:
+# ./page_alloc_stall.sh [hog_percent=80] [workers=64] [overcommit=2.5] \
+#                       [swap_gb=10%_RAM] [memtoy_path="memtoy/memtoy"]
+
+set -e
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+PYTHON_CMD=${PYTHON_CMD:-python3}
+
+HOG_PERCENT=${1:-80}
+NUM_WORKERS=${2:-64}
+OVERCOMMIT=${3:-2.5}
+TARGET_SWAP_GB=$4
+MEMTOY_PATH=${5:-"memtoy/memtoy"}
+
+function total_mem_gb()
+{
+    awk '/MemTotal/ {print int($2 / 1024 / 1024)}' /proc/meminfo
+}
+
+function enable_zswap_file()
+{
+    local swap_size_gb=$1
+
+    fallocate -l ${swap_size_gb}G "$SCRIPT_DIR/swap.img"
+
+    LOOP_DEV=$(losetup -f --show "$SCRIPT_DIR/swap.img")
+    mkswap $LOOP_DEV
+    swapon $LOOP_DEV
+
+    echo 1 > /sys/module/zswap/parameters/enabled
+}
+
+function cleanup()
+{
+    echo "Tearing down the test..."
+    if lsmod | grep -q test_mempress_timer; then
+        rmmod test_mempress_timer || echo "Failed to rmmod mempress_timer"
+    fi
+
+    # Check if loop dev was actually created before trying to destroy it
+    if [ -n "$LOOP_DEV" ]; then
+        swapoff $LOOP_DEV 2>/dev/null || true
+        losetup -d $LOOP_DEV 2>/dev/null || true
+    fi
+    rm -f "$SCRIPT_DIR/swap.img"
+}
+
+trap cleanup EXIT
+
+if [ -z "$TARGET_SWAP_GB" ]; then
+    # use 10% of the total mem for zswap file by default.
+    TARGET_SWAP_GB=$(($(total_mem_gb) / 10))
+fi
+
+enable_zswap_file $TARGET_SWAP_GB
+
+KROOT=$(cd "$SCRIPT_DIR/../../../.." && pwd)
+KO_PATH="$KROOT/lib/test_mempress_timer.ko"
+
+if [ "$KO_PATH" ]; then
+    insmod "$KO_PATH"
+else
+    echo "WARNING: $KO_PATH not found! Aborting the test."
+    exit 1
+fi
+
+"$PYTHON_CMD" "$SCRIPT_DIR/page_alloc_stall_pressure.py" $HOG_PERCENT $NUM_WORKERS $OVERCOMMIT $MEMTOY_PATH
-- 
2.55.0.691.gc56d675ccc-goog