Remove some dead code from SharedArrayPool (dotnet#101410)

In Trim, for high memory pressure, we're already setting the number of arrays to trim equal to the max number possible, so the subsequent logic that would increase the count wasn't useful. Deleting that also deleted the last use of _elementSize, which in turn allowed for the path that provided that value to be cleaned up.

Author: stephentoub

src/libraries/System.Private.CoreLib/src/System/Buffers/SharedArrayPool.cs

@@ -40,10 +40,7 @@ internal sealed partial class SharedArrayPool<T> : ArrayPool<T>
         /// <summary>Allocate a new <see cref="SharedArrayPoolPartitions"/> and try to store it into the <see cref="_buckets"/> array.</summary>
         private unsafe SharedArrayPoolPartitions CreatePerCorePartitions(int bucketIndex)
         {
-#pragma warning disable 8500 // sizeof of managed types
-            int elementSize = sizeof(T);
-#pragma warning restore 8500
-            var inst = new SharedArrayPoolPartitions(elementSize);
+            var inst = new SharedArrayPoolPartitions();
             return Interlocked.CompareExchange(ref _buckets[bucketIndex], inst, null) ?? inst;
         }
 
@@ -199,7 +196,7 @@ public bool Trim()
             SharedArrayPoolPartitions?[] perCoreBuckets = _buckets;
             for (int i = 0; i < perCoreBuckets.Length; i++)
             {
-                perCoreBuckets[i]?.Trim(currentMilliseconds, Id, pressure, Utilities.GetMaxSizeForBucket(i));
+                perCoreBuckets[i]?.Trim(currentMilliseconds, Id, pressure);
             }
 
             // Trim each of the TLS buckets. Note that threads may be modifying their TLS slots concurrently with
@@ -323,14 +320,13 @@ internal sealed class SharedArrayPoolPartitions
         private readonly Partition[] _partitions;
 
         /// <summary>Initializes the partitions.</summary>
-        /// <param name="elementSize">The size of the elements stored in arrays.</param>
-        public SharedArrayPoolPartitions(int elementSize)
+        public SharedArrayPoolPartitions()
         {
             // Create the partitions.  We create as many as there are processors, limited by our max.
             var partitions = new Partition[SharedArrayPoolStatics.s_partitionCount];
             for (int i = 0; i < partitions.Length; i++)
             {
-                partitions[i] = new Partition(elementSize);
+                partitions[i] = new Partition();
             }
             _partitions = partitions;
         }
@@ -374,23 +370,20 @@ public bool TryPush(Array array)
             return null;
         }
 
-        public void Trim(int currentMilliseconds, int id, Utilities.MemoryPressure pressure, int bucketSize)
+        public void Trim(int currentMilliseconds, int id, Utilities.MemoryPressure pressure)
         {
             Partition[] partitions = _partitions;
             for (int i = 0; i < partitions.Length; i++)
             {
-                partitions[i].Trim(currentMilliseconds, id, pressure, bucketSize);
+                partitions[i].Trim(currentMilliseconds, id, pressure);
             }
         }
 
         /// <summary>Provides a simple, bounded stack of arrays, protected by a lock.</summary>
-        /// <param name="elementSize">The size of the elements stored in arrays.</param>
-        private sealed class Partition(int elementSize)
+        private sealed class Partition
         {
             /// <summary>The arrays in the partition.</summary>
             private readonly Array?[] _arrays = new Array[SharedArrayPoolStatics.s_maxArraysPerPartition];
-            /// <summary>The size of the elements stored in arrays.</summary>
-            private readonly int _elementSize = elementSize;
             /// <summary>Number of arrays stored in <see cref="_arrays"/>.</summary>
             private int _count;
             /// <summary>Timestamp set by Trim when it sees this as 0.</summary>
@@ -437,20 +430,11 @@ public bool TryPush(Array array)
                 return arr;
             }
 
-            public void Trim(int currentMilliseconds, int id, Utilities.MemoryPressure pressure, int bucketSize)
+            public void Trim(int currentMilliseconds, int id, Utilities.MemoryPressure pressure)
             {
                 const int TrimAfterMS = 60 * 1000;                                  // Trim after 60 seconds for low/moderate pressure
                 const int HighTrimAfterMS = 10 * 1000;                              // Trim after 10 seconds for high pressure
 
-                const int LargeBucket = 16384;                                      // If the bucket is larger than this we'll trim an extra when under high pressure
-
-                const int ModerateTypeSize = 16;                                    // If T is larger than this we'll trim an extra when under high pressure
-                const int LargeTypeSize = 32;                                       // If T is larger than this we'll trim an extra (additional) when under high pressure
-
-                const int LowTrimCount = 1;                                         // Trim one item when pressure is low
-                const int MediumTrimCount = 2;                                      // Trim two items when pressure is moderate
-                int HighTrimCount = SharedArrayPoolStatics.s_maxArraysPerPartition; // Trim all items when pressure is high
-
                 if (_count == 0)
                 {
                     return;
@@ -477,38 +461,16 @@ public void Trim(int currentMilliseconds, int id, Utilities.MemoryPressure press
                     }
 
                     // We've elapsed enough time since the first item went into the partition.
-                    // Drop the top item so it can be collected and make the partition look a little newer.
+                    // Drop the top item(s) so they can be collected.
 
-                    ArrayPoolEventSource log = ArrayPoolEventSource.Log;
-                    int trimCount = LowTrimCount;
-                    switch (pressure)
+                    int trimCount = pressure switch
                     {
-                        case Utilities.MemoryPressure.High:
-                            trimCount = HighTrimCount;
-
-                            // When pressure is high, aggressively trim larger arrays.
-                            if (bucketSize > LargeBucket)
-                            {
-                                trimCount++;
-                            }
-
-                            if (_elementSize > ModerateTypeSize)
-                            {
-                                trimCount++;
-
-                                if (_elementSize > LargeTypeSize)
-                                {
-                                    trimCount++;
-                                }
-                            }
-
-                            break;
-
-                        case Utilities.MemoryPressure.Medium:
-                            trimCount = MediumTrimCount;
-                            break;
-                    }
+                        Utilities.MemoryPressure.High => SharedArrayPoolStatics.s_maxArraysPerPartition,
+                        Utilities.MemoryPressure.Medium => 2,
+                        _ => 1,
+                    };
 
+                    ArrayPoolEventSource log = ArrayPoolEventSource.Log;
                     while (_count > 0 && trimCount-- > 0)
                     {
                         Array? array = _arrays[--_count];