feat(virtio-pmem): add memory saving test

When VM is booted from virtio-pmem device with DAX,
it should use less guest page cache than VM booted
from virtio-block device

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse

tests/integration_tests/functional/test_pmem.py

@@ -6,6 +6,7 @@
 import os
 
 import host_tools.drive as drive_tools
+from framework import utils
 
 ALIGNMENT = 2 << 20
 
@@ -140,3 +141,66 @@ def test_pmem_add_as_root_ro(uvm_plain_any, rootfs, microvm_factory):
     snapshot = vm.snapshot_full()
     restored_vm = microvm_factory.build_from_snapshot(snapshot)
     check_pmem_exist(restored_vm, 0, True, True, align(rootfs_size), "squashfs")
+
+
+def inside_buff_cache(vm) -> int:
+    """Get buffer/cache usage from inside the vm"""
+    _, stdout, _ = vm.ssh.check_output("free")
+    # Get the `buffer/cache` of the `free` command which represents
+    # kernel page cache size
+    return int(stdout.splitlines()[1].split()[5])
+
+
+def outside_rssanon(vm) -> int:
+    """Get RssAnon usage from outside the vm"""
+    cmd = f"cat /proc/{vm.firecracker_pid}/status | grep RssAnon"
+    _, stdout, _ = utils.check_output(cmd)
+    return int(stdout.split()[1])
+
+
+def test_pmem_dax_memory_saving(
+    microvm_factory,
+    guest_kernel_acpi,
+    rootfs_rw,
+):
+    """
+    Test that booting from pmem with DAX enabled indeed saves memory in the
+    guest by not needing guest to use its page cache
+    """
+
+    # Boot from a block device
+    vm = microvm_factory.build(
+        guest_kernel_acpi, rootfs_rw, pci=True, monitor_memory=False
+    )
+    vm.spawn()
+    vm.basic_config()
+    vm.add_net_iface()
+    vm.start()
+    block_cache_usage = inside_buff_cache(vm)
+    block_rss_usage = outside_rssanon(vm)
+
+    # Boot from pmem with DAX enabled for root device
+    vm_pmem = microvm_factory.build(
+        guest_kernel_acpi, rootfs_rw, pci=True, monitor_memory=False
+    )
+    vm_pmem.spawn()
+    vm_pmem.basic_config(
+        add_root_device=False,
+        boot_args="reboot=k panic=1 nomodule swiotlb=noforce console=ttyS0 rootflags=dax",
+    )
+    vm_pmem.add_net_iface()
+    vm_pmem.add_pmem("pmem", rootfs_rw, True, False)
+    vm_pmem.start()
+    pmem_cache_usage = inside_buff_cache(vm_pmem)
+    pmem_rss_usage = outside_rssanon(vm_pmem)
+
+    # The pmem cache usage should be much lower than drive cache usage.
+    # The 50% is an arbitrary number, but does provide a good guarantee
+    # that DAX is working
+    assert (
+        pmem_cache_usage < block_cache_usage * 0.5
+    ), f"{block_cache_usage} <= {pmem_cache_usage}"
+    # RssAnon difference will be smaller, so no multipliers
+    assert (
+        pmem_rss_usage < block_rss_usage
+    ), f"{block_cache_usage} <= {pmem_cache_usage}"