Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1386635

vsintegration/src/FSharp.Editor/LanguageService/FSharpCheckerProvider.fs

@@ -5,6 +5,7 @@ namespace Microsoft.VisualStudio.FSharp.Editor
 open System
 open System.ComponentModel.Composition
 open System.Diagnostics
+open System.Reflection
 open Microsoft.CodeAnalysis
 open FSharp.Compiler
 open FSharp.Compiler.SourceCodeServices
@@ -64,6 +65,12 @@ type internal FSharpCheckerProvider
                     enableBackgroundItemKeyStoreAndSemanticClassification = false) // This option crashes on Mono due to MemoryMappedFile usage
                     //enablePartialTypeChecking = true)
 
+            // HACK: VSMAC - Set MaxMemoryReached flag to true to prevent repeated calls to GC.GetTotalMemory in service.fs CheckMaxMemoryReached which can be slow on Mono
+            // We can remove this hack once we have migrated to dotnet
+            let field = checker.GetType().GetField("maxMemoryReached", BindingFlags.NonPublic ||| BindingFlags.Instance)
+            field.SetValue(checker, true);
+
+
             // This is one half of the bridge between the F# background builder and the Roslyn analysis engine.
             // When the F# background builder refreshes the background semantic build context for a file,
             // we request Roslyn to reanalyze that individual file.