[release/10.0] Enable using CLRDATA_ENUM_MEM_HEAP2 through environment variable

src/coreclr/debug/daccess/enummem.cpp

@@ -2021,6 +2021,16 @@ ClrDataAccess::EnumMemoryRegions(IN ICLRDataEnumMemoryRegionsCallback* callback,
             {
                 DacLogMessage("EnumMemoryRegions(CLRDATA_ENUM_MEM_HEAP2)\n");
             }
+            else if (g_EnableFastHeapDumps != 0)
+            {
+                // When the target process had DOTNET_EnableFastHeapDumps set,
+                // use HEAP2 which dumps loader heap pages in bulk instead of
+                // walking individual runtime structures. This is significantly
+                // faster and produces equivalent dump content since all runtime
+                // data structures reside in loader heaps.
+                flags = CLRDATA_ENUM_MEM_HEAP2;
+                DacLogMessage("EnumMemoryRegions(CLRDATA_ENUM_MEM_HEAP promoted to HEAP2 via DOTNET_EnableFastHeapDumps)\n");
+            }
             else
             {
                 flags = CLRDATA_ENUM_MEM_HEAP;

src/coreclr/inc/clrconfigvalues.h

@@ -207,6 +207,7 @@ CONFIG_DWORD_INFO(UNSUPPORTED_Debugging_RequiredVersion, W("UNSUPPORTED_Debuggin
 #ifdef FEATURE_MINIMETADATA_IN_TRIAGEDUMPS
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_MiniMdBufferCapacity, W("MiniMdBufferCapacity"), 64 * 1024, "The max size of the buffer to store mini metadata information for triage- and mini-dumps.")
 #endif // FEATURE_MINIMETADATA_IN_TRIAGEDUMPS
+RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableFastHeapDumps, W("EnableFastHeapDumps"), 0, "If non-zero, uses CLRDATA_ENUM_MEM_HEAP2 for heap dumps which enumerates loader heap pages in bulk instead of walking individual runtime data structures.")
 
 CONFIG_DWORD_INFO(INTERNAL_DbgNativeCodeBpBindsAcrossVersions, W("DbgNativeCodeBpBindsAcrossVersions"), 0, "If non-zero causes native breakpoints at offset 0 to bind in all tiered compilation versions of the given method")
 RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RichDebugInfo, W("RichDebugInfo"), 0, "If non-zero store some additional debug information for each jitted method")

src/coreclr/inc/dacvars.h

@@ -184,6 +184,7 @@ DEFINE_DACVAR(bool, dac__g_fProcessDetach, ::g_fProcessDetach)
 DEFINE_DACVAR_VOLATILE(DWORD, dac__g_fEEShutDown, ::g_fEEShutDown)
 
 DEFINE_DACVAR(ULONG, dac__g_CORDebuggerControlFlags, ::g_CORDebuggerControlFlags)
+DEFINE_DACVAR(DWORD, dac__g_EnableFastHeapDumps, ::g_EnableFastHeapDumps)
 DEFINE_DACVAR(UNKNOWN_POINTER_TYPE, dac__g_pDebugger, ::g_pDebugger)
 DEFINE_DACVAR(UNKNOWN_POINTER_TYPE, dac__g_pDebugInterface, ::g_pDebugInterface)
 DEFINE_DACVAR(UNKNOWN_POINTER_TYPE, dac__g_pEEDbgInterfaceImpl, ::g_pEEDbgInterfaceImpl)

src/coreclr/vm/ceemain.cpp

@@ -639,7 +639,7 @@ void EEStartupHelper()
 
         IfFailGo(EEConfig::Setup());
 
-
+        g_EnableFastHeapDumps = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_EnableFastHeapDumps);
 #ifdef HOST_WINDOWS
         InitializeCrashDump();
 
@@ -2223,4 +2223,3 @@ void ContractRegressionCheck()
 }
 
 #endif // ENABLE_CONTRACTS_IMPL
-

src/coreclr/vm/vars.cpp

@@ -140,6 +140,7 @@ ETW::CEtwTracer * g_pEtwTracer = NULL;
 GPTR_IMPL(DebugInterface,     g_pDebugInterface);
 // A managed debugger may set this flag to high from out of process.
 GVAL_IMPL_INIT(DWORD,         g_CORDebuggerControlFlags, DBCF_NORMAL_OPERATION);
+GVAL_IMPL_INIT(DWORD,         g_EnableFastHeapDumps, 0);
 
 #ifdef DEBUGGING_SUPPORTED
 GPTR_IMPL(EEDbgInterfaceImpl, g_pEEDbgInterfaceImpl);

src/coreclr/vm/vars.hpp

@@ -409,6 +409,7 @@ GPTR_DECL(StressLog, g_pStressLog);
 //
 GPTR_DECL(DebugInterface,     g_pDebugInterface);
 GVAL_DECL(DWORD,              g_CORDebuggerControlFlags);
+GVAL_DECL(DWORD,              g_EnableFastHeapDumps);
 #ifdef DEBUGGING_SUPPORTED
 GPTR_DECL(EEDbgInterfaceImpl, g_pEEDbgInterfaceImpl);