Trim memory usage of IReadOnlyPackage implementations.

These implementations are often backed by a Dictionary, and tend to live a long time after being loaded. Ensure TrimExcess is called on the backing dictionaries to reduce the long term memory usage. In some cases, we can also preallocate the dictionary size for efficiency.

OpenRA.Mods.Cnc/FileSystem/BigFile.cs

@@ -25,7 +25,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 			public string Name { get; }
 			public IEnumerable<string> Contents => index.Keys;
 
-			readonly Dictionary<string, Entry> index = new();
+			readonly Dictionary<string, Entry> index;
 			readonly Stream s;
 
 			public BigFile(Stream s, string filename)
@@ -48,6 +48,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 					// and we don't have to try seeking there since the entries typically start next in EA's .big files.
 					s.ReadUInt32();
 
+					index = new Dictionary<string, Entry>((int)entryCount);
 					for (var i = 0; i < entryCount; i++)
 					{
 						var entry = new Entry(s);

OpenRA.Mods.Cnc/FileSystem/MegFile.cs

@@ -51,7 +51,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 		{
 			readonly Stream s;
 
-			readonly Dictionary<string, (uint Offset, int Length)> contents = new();
+			readonly Dictionary<string, (uint Offset, int Length)> contents;
 
 			public MegFile(Stream s, string filename)
 			{
@@ -84,6 +84,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 					throw new Exception("File name table in .meg file inconsistent");
 
 				// Now we load each file entry and associated info
+				contents = new Dictionary<string, (uint Offset, int Length)>((int)numFiles);
 				for (var i = 0; i < numFiles; i++)
 				{
 					// Ignore flags, crc, index
@@ -94,6 +95,8 @@ namespace OpenRA.Mods.Cnc.FileSystem
 					contents[filenames[nameIndex]] = (offset, (int)size);
 				}
 
+				contents.TrimExcess();
+
 				if (s.Position != headerSize)
 					throw new Exception("Expected to be at data start offset");
 			}

OpenRA.Mods.Cnc/FileSystem/MixFile.cs

@@ -66,8 +66,6 @@ namespace OpenRA.Mods.Cnc.FileSystem
 
 			Dictionary<string, PackageEntry> ParseIndex(Dictionary<uint, PackageEntry> entries, string[] globalFilenames)
 			{
-				var classicIndex = new Dictionary<string, PackageEntry>();
-				var crcIndex = new Dictionary<string, PackageEntry>();
 				var allPossibleFilenames = new HashSet<string>(globalFilenames);
 
 				// Try and find a local mix database
@@ -88,6 +86,9 @@ namespace OpenRA.Mods.Cnc.FileSystem
 					}
 				}
 
+				var classicIndex = new Dictionary<string, PackageEntry>(entries.Count);
+				var crcIndex = new Dictionary<string, PackageEntry>(entries.Count);
+
 				foreach (var filename in allPossibleFilenames)
 				{
 					var classicHash = PackageEntry.HashFilename(filename, PackageHashType.Classic);
@@ -106,6 +107,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 				if (unknown > 0)
 					Log.Write("debug", $"{Name}: failed to resolve filenames for {unknown} unknown hashes");
 
+				bestIndex.TrimExcess();
 				return bestIndex;
 			}
 

OpenRA.Mods.Cnc/FileSystem/Pak.cs

@@ -50,12 +50,11 @@ namespace OpenRA.Mods.Cnc.FileSystem
 						var length = (next == 0 ? (uint)stream.Length : next) - offset;
 
 						// Ignore duplicate files
-						if (index.ContainsKey(file))
-							continue;
-
-						index.Add(file, new Entry { Offset = offset, Length = length, Filename = file });
-						offset = next;
+						if (index.TryAdd(file, new Entry { Offset = offset, Length = length, Filename = file }))
+							offset = next;
 					}
+
+					index.TrimExcess();
 				}
 				catch
 				{

OpenRA.Mods.Common/FileSystem/InstallShieldPackage.cs

@@ -37,7 +37,7 @@ namespace OpenRA.Mods.Common.FileSystem
 			public string Name { get; }
 			public IEnumerable<string> Contents => index.Keys;
 
-			readonly Dictionary<string, Entry> index = new();
+			readonly Dictionary<string, Entry> index;
 			readonly Stream s;
 			readonly long dataStart = 255;
 
@@ -63,7 +63,8 @@ namespace OpenRA.Mods.Common.FileSystem
 					s.Position = tocAddress;
 
 					// Parse directories
-					var directories = new Dictionary<string, uint>();
+					var directories = new Dictionary<string, uint>(dirCount);
+					var totalFileCount = 0;
 					for (var i = 0; i < dirCount; i++)
 					{
 						// Parse directory header
@@ -75,12 +76,16 @@ namespace OpenRA.Mods.Common.FileSystem
 						// Skip to the end of the chunk
 						s.Position += chunkSize - nameLength - 6;
 						directories.Add(dirName, fileCount);
+						totalFileCount += fileCount;
 					}
 
 					// Parse files
+					index = new Dictionary<string, Entry>(totalFileCount);
 					foreach (var dir in directories)
 						for (var i = 0; i < dir.Value; i++)
 							ParseFile(dir.Key);
+
+					index.TrimExcess();
 				}
 				catch
 				{

OpenRA.Mods.D2k/PackageLoaders/D2kSoundResources.cs

@@ -54,6 +54,8 @@ namespace OpenRA.Mods.D2k.PackageLoaders
 						var length = s.ReadUInt32();
 						index.Add(name, new Entry(offset, length));
 					}
+
+					index.TrimExcess();
 				}
 				catch
 				{