Add GC.GetConfigVariable API, and support more GC settings in runtimeconfig

src/coreclr/src/System.Private.CoreLib/src/System/GC.cs

@@ -78,6 +78,47 @@ public static GCMemoryInfo GetGCMemoryInfo()
                                     fragmentedBytes: (long)(ulong)lastRecordedFragmentationBytes);
         }
 
+        [DllImport(RuntimeHelpers.QCall, CharSet = CharSet.Ansi)]
+        private static extern void GetGCConfigurationVariable(string name, StringHandleOnStack retString);
+
+        [MethodImpl(MethodImplOptions.InternalCall)]
+        private static extern string[] GetGCConfigurationVariables();
+
+        /// <summary>
+        /// Given the name of a GC configuration variable, get the set or default value.
+        /// </summary>
+        /// <remarks>
+        /// Returns `null` for an invalid name.
+        /// For a list of possible names, see the keys of `GetConfigurationVariables`.
+        ///
+        /// Numeric are in decimal even though environment variables are specified using hexadecimal.
+        ///
+        /// This reflects actually used values, not just explicit settings.
+        /// For example, if you set `System.GC.HeapCount` but not `System.GC.Server`,
+        /// the result for "HeapCount" would be "1" as workstation GC only uses 1 heap.
+        /// Similarly, "NoAffinitize" may be true if "HeapHardLimit" is set and HeapAffinitizeRanges is not.
+        /// </remarks>
+        public static string? GetConfigurationVariable(string name)
+        {
+            string result = "";
+            GetGCConfigurationVariable(name, new StringHandleOnStack(ref result));
+            return result == "" ? null : result;
+        }
+
+        /// <summary>
+        /// Returns all possible GC configuration variables and their values.
+        /// </summary>
+        /// <remarks>
+        /// See `GetConfigurationVariable` for description of how we get values.
+        /// </remarks>
+        public static IEnumerable<KeyValuePair<string, string>> GetConfigurationVariables()
+        {
+            foreach (string v in GetGCConfigurationVariables())
+            {
+                yield return new KeyValuePair<string, string>(v, GetConfigurationVariable(v)!);
+            }
+        }
+
         [DllImport(RuntimeHelpers.QCall, CharSet = CharSet.Unicode)]
         internal static extern int _StartNoGCRegion(long totalSize, bool lohSizeKnown, long lohSize, bool disallowFullBlockingGC);
 

src/coreclr/src/gc/gc.cpp

@@ -38815,6 +38815,121 @@ void GCHeap::GetMemoryInfo(uint64_t* highMemLoadThresholdBytes,
     *lastRecordedFragmentationBytes = gc_heap::last_gc_fragmentation;
 }
 
+static const char* bool_to_str(const bool value)
+{
+    const char* content = value ? "true" : "false";
+    const size_t len = strlen(content);
+    // + 1 for the '\0'
+    char* out = new (nothrow) char[len + 1];
+    if (out != nullptr)
+    {
+        strncpy(out, content, len + 1);
+        assert(out[len] == '\0' && strcmp(out, content) == 0);
+    }
+    return out;
+}
+
+static const char* int64_t_to_str(const int64_t value)
+{
+    // 2**64 in base ten has 20 characters at most, + 1 for the '\0'
+    const size_t max_size = 21;
+    char* out = new (nothrow) char[max_size];
+    if (out != nullptr)
+    {
+        int n = _snprintf_s (out, max_size, _TRUNCATE, "%llu", (long long) value);
+        // -1 because n does not include the '\0'
+        assert (n <= max_size - 1);
+    }
+    return out;
+}
+
+static char const* const configuration_variables[11] =
+{
+    "CpuGroup",
+    "HeapAffinitizeMask",
+    "HeapAffinitizeRanges",
+    "HeapCount",
+    "HeapHardLimit",
+    "HeapHardLimitPercent",
+    "HighMemoryPercent",
+    "LargePages",
+    "LOHThreshold",
+    "NoAffinitize",
+    "Server"
+};
+
+slice<char const* const> GCHeap::GetGCConfigurationVariables()
+{
+    return slice<char const* const>::FromArray<11>(configuration_variables);
+}
+
+const char* GCHeap::GetGCConfigurationVariable(const char* key)
+{
+    if (strcmp(key, "CpuGroup") == 0)
+    {
+        return bool_to_str(GCConfig::GetGCCpuGroup());
+    }
+    else if (strcmp(key, "HeapAffinitizeMask") == 0)
+    {
+        return int64_t_to_str(GCConfig::GetGCHeapAffinitizeMask());
+    }
+    else if (strcmp(key, "HeapAffinitizeRanges") == 0)
+    {
+        // GetGCHeapAffinitizeRanges returns a GCConfigStringHolder which will delete the string, but not if we Extract() it.
+        return GCConfig::GetGCHeapAffinitizeRanges().Extract();
+    }
+    else if (strcmp(key, "HeapCount") == 0)
+    {
+#ifdef MULTIPLE_HEAPS
+        const size_t heapCount = gc_heap::n_heaps;
+#else
+        const size_t heapCount = 1;
+#endif
+        return int64_t_to_str(heapCount);
+    }
+    else if (strcmp(key, "HeapHardLimit") == 0)
+    {
+        return int64_t_to_str(gc_heap::heap_hard_limit);
+    }
+    else if (strcmp(key, "HeapHardLimitPercent") == 0)
+    {
+        return int64_t_to_str(GCConfig::GetGCHeapHardLimitPercent());
+    }
+    else if (strcmp(key, "HighMemoryPercent") == 0)
+    {
+        return int64_t_to_str(gc_heap::high_memory_load_th);
+    }
+    else if (strcmp(key, "LargePages") == 0)
+    {
+        return bool_to_str(gc_heap::use_large_pages_p);
+    }
+    else if (strcmp(key, "LOHThreshold") == 0)
+    {
+        return int64_t_to_str(loh_size_threshold);
+    }
+    else if (strcmp(key, "NoAffinitize") == 0)
+    {
+#ifdef MULTIPLE_HEAPS
+        const bool noAffinitize = gc_heap::gc_thread_no_affinitize_p;
+#else
+        const bool noAffinitize = false;
+#endif
+        return bool_to_str(noAffinitize);
+    }
+    else if (strcmp(key, "Server") == 0)
+    {
+#ifdef MULTIPLE_HEAPS
+        return bool_to_str(true);
+#else
+        return bool_to_str(false);
+#endif
+    }
+    else
+    {
+        return nullptr;
+    }
+}
+
 int GCHeap::GetGcLatencyMode()
 {
     return (int)(pGenGCHeap->settings.pause_mode);

src/coreclr/src/gc/gcconfig.h

@@ -48,6 +48,14 @@ class GCConfigStringHolder
 
     // Retrieves the wrapped config string.
     const char* Get() const { return m_str; }
+
+    // Returns the wrapped config string and sets to null.
+    // Now the caller is responsible for freeing it.
+    const char* Extract() {
+        const char* result = m_str;
+        m_str = nullptr;
+        return result;
+    }
 };
 
 // Note that the configs starting BGCFLTuningEnabled ending BGCG2RatioStep are for BGC servo

src/coreclr/src/gc/gcimpl.h

@@ -177,6 +177,9 @@ class GCHeap : public IGCHeapInternal
                        uint32_t* lastRecordedMemLoadPct,
                        size_t* lastRecordedHeapSizeBytes,
                        size_t* lastRecordedFragmentationBytes);
+
+    const char* GetGCConfigurationVariable(const char* key);
+    slice<char const* const> GetGCConfigurationVariables();
 
     int GetGcLatencyMode();
     int SetGcLatencyMode(int newLatencyMode);

src/coreclr/src/gc/gcinterface.h

@@ -14,6 +14,32 @@
 // mismatches can still interopate correctly, with some care.
 #define GC_INTERFACE_MINOR_VERSION 1
 
+template <typename T>
+class slice {
+    T* _begin;
+    size_t _length;
+
+    slice(T* begin, size_t length) : _begin{begin}, _length{length} {}
+
+public:
+    template <size_t size>
+    static slice<T> FromArray(T data[size])
+    {
+        return slice<T> { data, size };
+    }
+
+    size_t size() const
+    {
+        return _length;
+    }
+
+    const T& operator[](size_t index) const
+    {
+        assert(index < _length);
+        return _begin[index];
+    }
+};
+
 struct ScanContext;
 struct gc_alloc_context;
 class CrawlFrame;
@@ -612,6 +638,9 @@ class IGCHeap {
                                size_t* lastRecordedHeapSizeBytes,
                                size_t* lastRecordedFragmentationBytes) = 0;
 
+    virtual const char* GetGCConfigurationVariable(const char* key) = 0;
+    virtual slice<char const* const> GetGCConfigurationVariables() = 0;
+
     // Gets the current GC latency mode.
     virtual int GetGcLatencyMode() = 0;
 

src/coreclr/src/inc/clrconfigvalues.h

@@ -315,7 +315,7 @@ RETAIL_CONFIG_STRING_INFO(EXTERNAL_GCName, W("GCName"), "")
 RETAIL_CONFIG_DWORD_INFO_DIRECT_ACCESS(EXTERNAL_GCHeapHardLimit, W("GCHeapHardLimit"), "Specifies the maximum commit size for the GC heap")
 RETAIL_CONFIG_DWORD_INFO_DIRECT_ACCESS(EXTERNAL_GCHeapHardLimitPercent, W("GCHeapHardLimitPercent"), "Specifies the GC heap usage as a percentage of the total memory")
 RETAIL_CONFIG_STRING_INFO(EXTERNAL_GCHeapAffinitizeRanges, W("GCHeapAffinitizeRanges"), "Specifies list of processors for Server GC threads. The format is a comma separated list of processor numbers or ranges of processor numbers. Example: 1,3,5,7-9,12")
-RETAIL_CONFIG_DWORD_INFO_DIRECT_ACCESS(EXTERNAL_GCLargePages, W("GCLargePages"), "Specifies whether large pages should be used when a heap hard limit is set")
+RETAIL_CONFIG_DWORD_INFO(EXTERNAL_GCLargePages, W("GCLargePages"), 0, "Specifies whether large pages should be used when a heap hard limit is set")
 
 ///
 /// IBC

src/coreclr/src/inc/holder.h

@@ -1028,6 +1028,7 @@ FORCEINLINE void DeleteArray(TYPE *value)
 
 NEW_WRAPPER_TEMPLATE1(NewArrayHolder, DeleteArray<_TYPE>);
 typedef NewArrayHolder<CHAR>  AStringHolder;
+typedef NewArrayHolder<const CHAR> AConstStringHolder;
 typedef NewArrayHolder<WCHAR> WStringHolder;
 
 //-----------------------------------------------------------------------------

src/coreclr/src/utilcode/util.cpp

@@ -20,6 +20,8 @@
 #include "corinfo.h"
 #include "volatile.h"
 
+#include "../inc/configuration.h"
+
 #ifndef DACCESS_COMPILE
 UINT32 g_nClrInstanceId = 0;
 #endif //!DACCESS_COMPILE
@@ -989,7 +991,7 @@ DWORD LCM(DWORD u, DWORD v)
     CONTRACTL_END;
 
 #if !defined(FEATURE_REDHAWK) && (defined(_TARGET_AMD64_) || defined(_TARGET_ARM64_))
-    BOOL enableGCCPUGroups     = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_GCCpuGroup) != 0;
+    BOOL enableGCCPUGroups     = Configuration::GetKnobBooleanValue(W("System.GC.CpuGroup"), CLRConfig::EXTERNAL_GCCpuGroup);
     BOOL threadUseAllCpuGroups = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_Thread_UseAllCpuGroups) != 0;
 
     if (!enableGCCPUGroups)

src/coreclr/src/vm/comutilnative.cpp

@@ -696,6 +696,43 @@ FCIMPL6(void, GCInterface::GetMemoryInfo, UINT64* highMemLoadThreshold, UINT64*
 }
 FCIMPLEND
 
+void QCALLTYPE GCInterface::GetGCConfigurationVariable(const char* key, QCall::StringHandleOnStack result)
+{
+    QCALL_CONTRACT;
+
+    BEGIN_QCALL;
+
+    AConstStringHolder value;
+    value = GCHeapUtilities::GetGCHeap()->GetGCConfigurationVariable(key);
+    if (value)
+    {
+        result.Set(value);
+    }
+
+    END_QCALL;
+}
+
+FCIMPL0(Object*, GCInterface::GetGCConfigurationVariables)
+{
+    FCALL_CONTRACT;
+
+    slice<char const* const> configVariables = GCHeapUtilities::GetGCHeap()->GetGCConfigurationVariables();
+
+    PTRARRAYREF strArray = NULL;
+    HELPER_METHOD_FRAME_BEGIN_RET_1(strArray);
+    strArray = (PTRARRAYREF) AllocateObjectArray(static_cast<DWORD>(configVariables.size()), g_pStringClass);
+    for (unsigned int i = 0; i < configVariables.size(); i++)
+    {
+        STRINGREF str = StringObject::NewString(configVariables[i]); // This copies it
+        STRINGREF * destData = ((STRINGREF*)(strArray->GetDataPtr())) + i;
+        SetObjectReference((OBJECTREF*)destData, (OBJECTREF)str);
+    }
+
+    HELPER_METHOD_FRAME_END();
+    return OBJECTREFToObject(strArray);
+}
+FCIMPLEND
+
 FCIMPL0(int, GCInterface::GetGcLatencyMode)
 {
     FCALL_CONTRACT;

src/coreclr/src/vm/comutilnative.h

@@ -97,6 +97,9 @@ class GCInterface {
     static FORCEINLINE UINT64 InterlockedSub(UINT64 *pMinuend, UINT64 subtrahend);
 
     static FCDECL6(void,    GetMemoryInfo, UINT64* highMemLoadThresholdBytes, UINT64* totalAvailableMemoryBytes, UINT64* lastRecordedMemLoadBytes, UINT32* lastRecordedMemLoadPct, size_t* lastRecordedHeapSizBytes, size_t* lastRecordedFragmentationBytes);
+    static void QCALLTYPE GetGCConfigurationVariable(const char* key, QCall::StringHandleOnStack result);
+    // The object will be a string[]
+    static FCDECL0(Object*, GetGCConfigurationVariables);
     static FCDECL0(int,     GetGcLatencyMode);
     static FCDECL1(int,     SetGcLatencyMode, int newLatencyMode);
     static FCDECL0(int,     GetLOHCompactionMode);

src/coreclr/src/vm/ecalllist.h

@@ -741,6 +741,8 @@ FCFuncStart(gGCInterfaceFuncs)
     QCFuncElement("_StartNoGCRegion", GCInterface::StartNoGCRegion)
     QCFuncElement("_EndNoGCRegion", GCInterface::EndNoGCRegion)
     FCFuncElement("GetSegmentSize", GCInterface::GetSegmentSize)
+    QCFuncElement("GetGCConfigurationVariable", GCInterface::GetGCConfigurationVariable)
+    FCFuncElement("GetGCConfigurationVariables", GCInterface::GetGCConfigurationVariables)
     FCFuncElement("GetLastGCPercentTimeInGC", GCInterface::GetLastGCPercentTimeInGC)
     FCFuncElement("GetGenerationSize", GCInterface::GetGenerationSize)
     QCFuncElement("_AddMemoryPressure", GCInterface::_AddMemoryPressure)

src/coreclr/src/vm/eeconfig.cpp

@@ -814,12 +814,18 @@ fTrackDynamicMethodDebugInfo = CLRConfig::GetConfigValue(CLRConfig::UNSUPPORTED_
     if (!iGCgen0size) iGCgen0size = GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_GCgen0size, iGCgen0size);
 #endif //BIT64
 
-    const ULONGLONG ullHeapHardLimit = Configuration::GetKnobULONGLONGValue(W("System.GC.HeapHardLimit"));
+    ULONGLONG ullHeapHardLimit = Configuration::GetKnobULONGLONGValue(W("System.GC.HeapHardLimit"));
+    if (!ullHeapHardLimit) ullHeapHardLimit = GetConfigULONGLONG_DontUse_(CLRConfig::EXTERNAL_GCHeapHardLimit, 0);
     iGCHeapHardLimit = FitsIn<size_t, ULONGLONG>(ullHeapHardLimit)
         ? static_cast<size_t>(ullHeapHardLimit)
         : ClrSafeInt<size_t>::MaxInt();
     iGCHeapHardLimitPercent = Configuration::GetKnobDWORDValue(W("System.GC.HeapHardLimitPercent"), 0);
 
+    iGCCpuGroup = Configuration::GetKnobBooleanValue(W("System.GC.CpuGroup"), CLRConfig::EXTERNAL_GCCpuGroup);
+    iGCHighMemoryPercent = Configuration::GetKnobDWORDValue(W("System.GC.HighMemoryPercent"), CLRConfig::EXTERNAL_GCHighMemPercent);
+    fGCLargePages = Configuration::GetKnobBooleanValue(W("System.GC.LargePages"), CLRConfig::EXTERNAL_GCLargePages);
+    lpszGCHeapAffinitizeRanges = Configuration::GetKnobStringValue(W("System.GC.HeapAffinitizeRanges"), CLRConfig::EXTERNAL_GCHeapAffinitizeRanges);
+
     if (g_IGCHoardVM)
         iGCHoardVM = g_IGCHoardVM;
     else

src/coreclr/src/vm/eeconfig.h

@@ -612,8 +612,12 @@ class EEConfig
     int     GetGCHeapCount()                const {LIMITED_METHOD_CONTRACT; return iGCHeapCount;}
     int     GetGCNoAffinitize ()            const {LIMITED_METHOD_CONTRACT; return iGCNoAffinitize;}
     size_t  GetGCAffinityMask()             const {LIMITED_METHOD_CONTRACT; return iGCAffinityMask;}
+    LPCWSTR GetGCHeapAffinitizeRanges()     const {LIMITED_METHOD_CONTRACT; return lpszGCHeapAffinitizeRanges;}
+    int     GetGCHighMemoryPercent()        const {LIMITED_METHOD_CONTRACT; return iGCHighMemoryPercent;}
     size_t  GetGCHeapHardLimit()            const {LIMITED_METHOD_CONTRACT; return iGCHeapHardLimit;}
     int     GetGCHeapHardLimitPercent()     const {LIMITED_METHOD_CONTRACT; return iGCHeapHardLimitPercent;}
+    bool    GetGCLargePages()               const {LIMITED_METHOD_CONTRACT; return fGCLargePages;}
+    bool    GetGCCpuGroup()                 const {LIMITED_METHOD_CONTRACT; return iGCCpuGroup;}
 
 #ifdef GCTRIMCOMMIT
 
@@ -917,8 +921,13 @@ class EEConfig
     int  iGCHeapCount;
     int  iGCNoAffinitize;
     size_t  iGCAffinityMask;
+    bool iGCCpuGroup;
+    // this points to a string from GetKnobStringValue and should not be freed.
+    LPCWSTR lpszGCHeapAffinitizeRanges;
+    int iGCHighMemoryPercent;
     size_t iGCHeapHardLimit;
     int iGCHeapHardLimitPercent;
+    bool fGCLargePages;
 
 #ifdef GCTRIMCOMMIT