Take review into account

src/coreclr/vm/ClrEtwAll.man

@@ -467,8 +467,6 @@
                           value="40" eventGUID="{CC82530E-A21C-4EB0-A68A-FA4F7E66498F}"
                           message="$(string.RuntimePublisher.AllocationSamplingTaskMessage)">
                         <opcodes>
-                            <!-- TODO: I don't know which value should be picked for this opcode-->
-                            <opcode name="AllocationSampled" message="$(string.RuntimePublisher.AllocationSampledOpcodeMessage)" symbol="CLR_ALLOCATIONSAMPLED_OPCODE" value="11"> </opcode>
                         </opcodes>
                     </task>
                 <!--Next available ID is 41-->
@@ -3175,7 +3173,6 @@
                     </template>
 
                     <template tid="AllocationSampled">
-                        <!--TODO: is it a problem to reuse the GC allocation kind?-->
                         <data name="AllocationKind" inType="win:UInt32" map="GCAllocationKindMap" />
                         <data name="ClrInstanceID" inType="win:UInt16" />
                         <data name="TypeID" inType="win:Pointer" />
@@ -4292,7 +4289,7 @@
 
                     <!-- Allocation sampling events -->
                     <event value="303" version="0" level="win:Informational" template="AllocationSampled"
-                           keywords="AllocationSamplingKeyword" opcode="AllocationSampled"
+                           keywords="AllocationSamplingKeyword"
                            task="AllocationSampling"
                            symbol="AllocationSampled" message="$(string.RuntimePublisher.AllocationSampledEventMessage)"/>
 
@@ -9331,7 +9328,6 @@
                 <string id="RuntimePublisher.ExecutionCheckpointOpcodeMessage" value="ExecutionCheckpoint" />
 
                 <string id="RuntimePublisher.ProfilerOpcodeMessage" value="ProfilerMessage" />
-                <string id="RuntimePublisher.AllocationSampledOpcodeMessage" value="AllocationSampled" />
 
                 <string id="RundownPublisher.GCSettingsOpcodeMessage" value="GCSettingsRundown" />
 

src/coreclr/vm/gcenv.ee.cpp

@@ -451,23 +451,21 @@ void InvokeGCAllocCallback(ee_alloc_context* pEEAllocContext, enum_alloc_context
 
     // The allocation context might be modified by the callback, so we need to save
     // the remaining sampling budget and restore it after the callback if needed.
-    size_t currentSamplingBudget = (pEEAllocContext->alloc_sampling == nullptr) ? -1 : (size_t)(pEEAllocContext->alloc_sampling - pAllocContext->alloc_ptr);
-    size_t currentSize = pAllocContext->alloc_limit - pAllocContext->alloc_ptr;
+    size_t currentSamplingBudget = (size_t)(pEEAllocContext->alloc_sampling - pAllocContext->alloc_ptr);
+    size_t currentSize = (size_t)(pAllocContext->alloc_limit - pAllocContext->alloc_ptr);
 
     fn(pAllocContext, param);
 
-    if (currentSamplingBudget != -1)
+    // If the GC changed the size of the allocation context, we need to recompute the sampling limit
+    // This includes the case where the AC was initially zero-sized/uninitialized.
+    if (currentSize != (size_t)(pAllocContext->alloc_limit - pAllocContext->alloc_ptr))
     {
-        // if the GC changed the size of the allocation context, we need to recompute the sampling limit
-        if (currentSize != (size_t)(pAllocContext->alloc_limit - pAllocContext->alloc_ptr))
-        {
-            pEEAllocContext->ComputeSamplingLimit(GetThread()->GetRandom());
-        }
-        else
-        {
-            // restore the remaining sampling budget when the GC simply moved the allocation context in memory
-            pEEAllocContext->alloc_sampling = pAllocContext->alloc_ptr + currentSamplingBudget;
-        }
+        pEEAllocContext->ComputeSamplingLimit(GetThread()->GetRandom());
+    }
+    else
+    {
+        // Restore the remaining sampling budget as the size is the same.
+        pEEAllocContext->alloc_sampling = pAllocContext->alloc_ptr + currentSamplingBudget;
     }
 }
 

src/coreclr/vm/gcheaputilities.h

@@ -45,20 +45,20 @@ typedef struct _ee_alloc_context
         // If sampling is on then we'd do some pseudo-random number generation to decide what is
         // the next sampled byte in the gc_alloc_context, if any.
 
-        // compute the next sampling limit based on an exponential distribution
-        size_t threshold = ComputeExponetialRandom(pRandomizer);
+        // compute the next sampling limit based on a geometric distribution
+        size_t threshold = ComputeExponentialRandom(pRandomizer);
 
         // if the threshold is larger than the allocation context, no sampling will occur
         alloc_sampling = Min(gc_alloc_context.alloc_ptr + threshold, gc_alloc_context.alloc_limit);
     }
 
     static inline bool IsSampled(CLRRandom* pRandomizer, size_t range)
     {
-        size_t threshold = ComputeExponetialRandom(pRandomizer);
+        size_t threshold = ComputeExponentialRandom(pRandomizer);
         return (threshold < range);
     }
 private:
-    static inline size_t ComputeExponetialRandom(CLRRandom* pRandomizer)
+    static inline size_t ComputeExponentialRandom(CLRRandom* pRandomizer)
     {
         // compute a thres based on an exponential distribution
         double probability = pRandomizer->NextDouble();

src/coreclr/vm/gchelpers.cpp

@@ -248,8 +248,6 @@ inline Object* Alloc(ee_alloc_context* pEEAllocContext, size_t size, GC_ALLOC_FL
     // only SOH allocations require sampling threshold to be recomputed
     if ((flags & GC_ALLOC_USER_OLD_HEAP) == 0)
     {
-        // the sampling threshold was crossed, so compute a new one (even if some
-        // free space is left in the allocation context)
         pEEAllocContext->ComputeSamplingLimit(pCurrentThread->GetRandom());
     }