Set page_reporting_order via kernel command line (#40374)
* Set page_reporting_order via kernel command line Move page reporting configuration from post-boot process launches and init messages to the kernel command line parameter (page_reporting.page_reporting_order=N). This ensures the correct order is set at boot time for both WSLC and WSL2. Remove PageReportingOrder from the early config message struct. Simplify the memory reduction thread in init to always perform compaction when idle, removing the PageReportingOrder gate which was effectively dead code (the value was always non-zero in practice). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Address PR feedback: simplify lambda capture and align page reporting logic - Simplify [Mode = Mode] to [Mode] in ConfigureMemoryReduction lambda - Use coldDiscardShiftSize variable in HcsVirtualMachine to match WslCoreVm pattern Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Ben Hillis committed
May 1, 2026 at 12:46 UTC
2cfdd58286cc41ef6f31280dd13bca8d8e574034
6 files changed
+29
-59
src/linux/init/main.cpp
+10
-36
@@ -122,7 +122,7 @@ std::optional<bool> g_EnableSocketLogging;
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int Chroot(const char* Target);
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-void ConfigureMemoryReduction(int PageReportingOrder, LX_MINI_INIT_MEMORY_RECLAIM_MODE Mode);
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+void ConfigureMemoryReduction(LX_MINI_INIT_MEMORY_RECLAIM_MODE Mode);
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void CreateSwap(unsigned int Lun);
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@@ -265,20 +265,16 @@ Return Value:
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return 0;
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}
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-void ConfigureMemoryReduction(int PageReportingOrder, LX_MINI_INIT_MEMORY_RECLAIM_MODE Mode)
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+void ConfigureMemoryReduction(LX_MINI_INIT_MEMORY_RECLAIM_MODE Mode)
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/*++
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Routine Description:
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- This routine sets the page reporting order.
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+ This routine configures memory reduction behavior including memory reclaim and compaction.
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Arguments:
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- PageReportingOrder - Supplies the page reporting order. This value determines the size of cold discard hints
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- by using the equation: 2^PageReportingOrder * PAGE_SIZE
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- Example: 2^9 * 4096 = 2MB
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-
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Mode - Supplies the memory reclaim mode.
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Return Value:
@@ -290,32 +286,11 @@ Return Value:
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try
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{
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//
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- // Ensure the value falls within a reasonable range (single page to 2MB).
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- //
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-
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- if (PageReportingOrder < 0 || PageReportingOrder > 9)
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- {
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- LOG_WARNING("Invalid page_reporting_order {}", PageReportingOrder);
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- PageReportingOrder = 0;
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- }
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- else
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- {
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- WriteToFile("/sys/module/page_reporting/parameters/page_reporting_order", std::to_string(PageReportingOrder).c_str());
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- }
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-
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- //
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- // Create a worker thread to periodically check if the VM is idle and performs memory compaction.
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- // This ensures that the maximum number of pages can be discarded to the host.
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+ // Create a worker thread to periodically check if the VM is idle and performs memory compaction
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+ // and memory reclaim. This ensures that the maximum number of pages can be discarded to the host.
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//
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- // N.B. Compaction is not needed if page reporting order is set to single page mode.
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- //
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-
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- if (PageReportingOrder == 0 && Mode == LxMiniInitMemoryReclaimModeDisabled)
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- {
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- return;
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- }
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- std::thread([PageReportingOrder = PageReportingOrder, Mode = Mode]() mutable {
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+ std::thread([Mode]() mutable {
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try
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{
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//
@@ -422,11 +397,10 @@ try
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//
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// Perform memory compaction if the VM is idle.
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- //
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- // N.B. Memory compaction is not needed if the page reporting order is set to single page (0).
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+ // This coalesces free pages into larger blocks for more efficient page reporting.
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//
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- if (PageReportingOrder != 0 && (Start - Stop) > IdleThreshold)
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+ if ((Start - Stop) > IdleThreshold)
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{
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std::this_thread::sleep_for(std::chrono::seconds(1));
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Stop = GetUserCpuTime();
@@ -3294,10 +3268,10 @@ try
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}
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//
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- // Configure page reporting and memory reclamation.
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+ // Configure memory reclamation.
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//
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- ConfigureMemoryReduction(EarlyConfig->PageReportingOrder, EarlyConfig->MemoryReclaimMode);
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+ ConfigureMemoryReduction(EarlyConfig->MemoryReclaimMode);
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//
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// Initialize system distro if supported.
src/shared/inc/lxinitshared.h
-2
@@ -1251,7 +1251,6 @@ typedef struct _LX_MINI_INIT_EARLY_CONFIG_MESSAGE
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unsigned int SwapLun;
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LX_MINI_INIT_MOUNT_DEVICE_TYPE SystemDistroDeviceType;
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unsigned int SystemDistroDeviceId;
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- int PageReportingOrder;
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LX_MINI_INIT_MEMORY_RECLAIM_MODE MemoryReclaimMode;
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// IPv4 address stored in network byte order
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uint32_t DnsTunnelingIpAddress = 0;
@@ -1269,7 +1268,6 @@ typedef struct _LX_MINI_INIT_EARLY_CONFIG_MESSAGE
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FIELD(SwapLun),
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FIELD(SystemDistroDeviceType),
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FIELD(SystemDistroDeviceId),
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- FIELD(PageReportingOrder),
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FIELD(MemoryReclaimMode),
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FIELD(DnsTunnelingIpAddress),
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FIELD(EnableDebugShell),
src/windows/service/exe/HcsVirtualMachine.cpp
+11
-2
@@ -76,15 +76,21 @@ HcsVirtualMachine::HcsVirtualMachine(_In_ const WSLCSessionSettings* Settings)
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vmSettings.ComputeTopology.Memory.EnableColdDiscardHint = true;
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vmSettings.ComputeTopology.Processor.Count = Settings->CpuCount;
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- // Configure backing page size, fault cluster shift size, and cold discard hint size to favor density (lower vmmem usage).
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+ // Configure backing page size, fault cluster shift size, and page reporting order to favor density (lower vmmem usage).
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//
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- // N.B. Cold discard hint size should be a multiple of the fault cluster shift size.
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+ // N.B. Page reporting order must be >= fault cluster size shift.
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const auto windowsVersion = wsl::windows::common::helpers::GetWindowsVersion();
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+ int pageReportingOrder;
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if (windowsVersion.BuildNumber >= WindowsBuildNumbers::Germanium)
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{
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vmSettings.ComputeTopology.Memory.BackingPageSize = hcs::MemoryBackingPageSize::Small;
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vmSettings.ComputeTopology.Memory.FaultClusterSizeShift = 4;
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vmSettings.ComputeTopology.Memory.DirectMapFaultClusterSizeShift = 4;
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+ pageReportingOrder = 5; // 128k
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+ }
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+ else
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+ {
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+ pageReportingOrder = 9; // 2MB
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}
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if (helpers::IsVmemmSuffixSupported() && Settings->DisplayName)
@@ -108,6 +114,9 @@ HcsVirtualMachine::HcsVirtualMachine(_In_ const WSLCSessionSettings* Settings)
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// Enable timesync workaround to sync on resume from sleep in modern standby.
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kernelCmdLine += L" hv_utils.timesync_implicit=1";
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+ // Configure page reporting order - minimum order of pages reported as free to the hypervisor.
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+ kernelCmdLine += std::format(L" page_reporting.page_reporting_order={}", pageReportingOrder);
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+
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// Setup dmesg collector with optional DmesgOutput handle.
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// TODO: move dmesg collector to user session process.
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// N.B. 'DmesgOutput' needs to be duplicated since COM will close it when this call completes.
src/windows/service/exe/WslCoreVm.cpp
+7
-5
@@ -509,7 +509,6 @@ void WslCoreVm::Initialize(const GUID& VmId, const wil::shared_handle& UserToken
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message->SwapLun = swapLun;
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message->SystemDistroDeviceType = m_systemDistroDeviceType;
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message->SystemDistroDeviceId = m_systemDistroDeviceId;
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- message->PageReportingOrder = m_coldDiscardShiftSize;
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message->MemoryReclaimMode = static_cast<LX_MINI_INIT_MEMORY_RECLAIM_MODE>(m_vmConfig.MemoryReclaim);
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message->EnableDebugShell = m_vmConfig.EnableDebugShell;
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message->EnableSafeMode = m_vmConfig.EnableSafeMode;
@@ -1381,9 +1380,9 @@ std::wstring WslCoreVm::GenerateConfigJson()
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vmSettings.ComputeTopology.Memory.EnableDeferredCommit = true;
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vmSettings.ComputeTopology.Memory.EnableColdDiscardHint = true;
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- // Configure backing page size, fault cluster shift size, and cold discard hint size to favor density (lower vmmem usage).
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+ // Configure backing page size, fault cluster shift size, and page reporting order to favor density (lower vmmem usage).
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//
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- // N.B. Cold discard hint size should be a multiple of the fault cluster shift size.
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+ // N.B. Page reporting order must be >= fault cluster size shift.
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//
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// N.B. This is only done on builds that have the fix for the VID deadlock on partition teardown.
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if ((m_windowsVersion.BuildNumber >= WindowsBuildNumbers::Germanium) ||
@@ -1394,11 +1393,11 @@ std::wstring WslCoreVm::GenerateConfigJson()
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vmSettings.ComputeTopology.Memory.BackingPageSize = hcs::MemoryBackingPageSize::Small;
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vmSettings.ComputeTopology.Memory.FaultClusterSizeShift = 4; // 64k
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vmSettings.ComputeTopology.Memory.DirectMapFaultClusterSizeShift = 4; // 64k
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- m_coldDiscardShiftSize = 5; // 128k
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+ m_pageReportingOrder = 5; // 128k
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}
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else
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{
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- m_coldDiscardShiftSize = 9; // 2MB
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+ m_pageReportingOrder = 9; // 2MB
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}
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// May need more MMIO than the default 16GB. WSL uses a vpci device per Plan9 share, WSLg adds a GPU device,
@@ -1527,6 +1526,9 @@ std::wstring WslCoreVm::GenerateConfigJson()
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// Enable timesync workaround to sync on resume from sleep in modern standby.
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kernelCmdLine += L" hv_utils.timesync_implicit=1";
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+ // Configure page reporting order - minimum order of pages reported as free to the hypervisor.
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+ kernelCmdLine += std::format(L" page_reporting.page_reporting_order={}", m_pageReportingOrder);
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+
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// If using virtio features, enable SWIOTLB as a perf optimization (will cause VM to consume 64MB more memory).
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if (m_vmConfig.EnableVirtio9p || m_vmConfig.EnableVirtioFs || m_vmConfig.NetworkingMode == NetworkingMode::VirtioProxy)
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{
src/windows/service/exe/WslCoreVm.h
+1
-1
@@ -277,7 +277,7 @@ private:
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wsl::core::Config m_vmConfig;
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std::wstring m_comPipe0;
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std::wstring m_comPipe1;
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- int m_coldDiscardShiftSize;
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+ int m_pageReportingOrder;
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WslTraceLoggingClient m_traceClient;
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std::filesystem::path m_rootFsPath;
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std::filesystem::path m_tempPath;
src/windows/wslcsession/WSLCVirtualMachine.cpp
-13
@@ -295,19 +295,6 @@ void WSLCVirtualMachine::Initialize()
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// Configure GPU mounts if enabled
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MountGpuLibraries(c_gpuLibrariesPath, c_gpuDriversPath);
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- // Configure cold discard hint size for page reporting.
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- // This sets the minimum order of pages that will be reported as free to the hypervisor.
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- {
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- const auto windowsVersion = wsl::windows::common::helpers::GetWindowsVersion();
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- int pageReportingOrder = (windowsVersion.BuildNumber >= wsl::windows::common::helpers::WindowsBuildNumbers::Germanium) ? 5 : 9; // 128k or 2MB
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- auto cmdStr = std::format("echo {} > /sys/module/page_reporting/parameters/page_reporting_order", pageReportingOrder);
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- std::vector<const char*> args{"/bin/sh", "-c", cmdStr.c_str()};
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-
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- WSLCProcessOptions options{};
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- options.CommandLine = {.Values = args.data(), .Count = static_cast<ULONG>(args.size())};
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- CreateLinuxProcessImpl("/bin/sh", options, {}, nullptr, [](const auto&) {});
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- }
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-
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// Configure networking. This must happen after all filesystems are mounted since /gns needs to access /sys.
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ConfigureNetworking();
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}