diff --git a/clang-tools-extra/clangd/TUScheduler.h b/clang-tools-extra/clangd/TUScheduler.h
--- a/clang-tools-extra/clangd/TUScheduler.h
+++ b/clang-tools-extra/clangd/TUScheduler.h
@@ -14,6 +14,7 @@
 #include "GlobalCompilationDatabase.h"
 #include "index/CanonicalIncludes.h"
 #include "support/Function.h"
+#include "support/MemoryTree.h"
 #include "support/Path.h"
 #include "support/Threading.h"
 #include "llvm/ADT/Optional.h"
@@ -207,7 +208,8 @@
   ~TUScheduler();
 
   struct FileStats {
-    std::size_t UsedBytes = 0;
+    std::size_t UsedBytesAST = 0;
+    std::size_t UsedBytesPreamble = 0;
     unsigned PreambleBuilds = 0;
     unsigned ASTBuilds = 0;
   };
@@ -311,6 +313,8 @@
   // FIXME: move to ClangdServer via createProcessingContext.
   static llvm::Optional<llvm::StringRef> getFileBeingProcessedInContext();
 
+  MemoryTree getMemoryUsage() const;
+
 private:
   const GlobalCompilationDatabase &CDB;
   Options Opts;
diff --git a/clang-tools-extra/clangd/TUScheduler.cpp b/clang-tools-extra/clangd/TUScheduler.cpp
--- a/clang-tools-extra/clangd/TUScheduler.cpp
+++ b/clang-tools-extra/clangd/TUScheduler.cpp
@@ -56,6 +56,7 @@
 #include "support/Cancellation.h"
 #include "support/Context.h"
 #include "support/Logger.h"
+#include "support/MemoryTree.h"
 #include "support/Path.h"
 #include "support/Threading.h"
 #include "support/Trace.h"
@@ -164,6 +165,19 @@
     return llvm::Optional<std::unique_ptr<ParsedAST>>(std::move(V));
   }
 
+  MemoryTree getMemoryUsage() const {
+    MemoryTree MT;
+    std::lock_guard<std::mutex> Lock(Mut);
+    for (const auto &Elem : LRU) {
+      auto &SM = Elem.second->getSourceManager();
+      MT.addChild(
+          // FIXME: Store the filename directly in the cache or ParsedAST.
+          SM.getFileEntryForID(SM.getMainFileID())->tryGetRealPathName(),
+          Elem.second->getUsedBytes());
+    }
+    return MT;
+  }
+
 private:
   using KVPair = std::pair<Key, std::unique_ptr<ParsedAST>>;
 
@@ -171,7 +185,7 @@
     return llvm::find_if(LRU, [K](const KVPair &P) { return P.first == K; });
   }
 
-  std::mutex Mut;
+  mutable std::mutex Mut;
   unsigned MaxRetainedASTs;
   /// Items sorted in LRU order, i.e. first item is the most recently accessed
   /// one.
@@ -932,9 +946,9 @@
   // Note that we don't report the size of ASTs currently used for processing
   // the in-flight requests. We used this information for debugging purposes
   // only, so this should be fine.
-  Result.UsedBytes = IdleASTs.getUsedBytes(this);
+  Result.UsedBytesAST = IdleASTs.getUsedBytes(this);
   if (auto Preamble = getPossiblyStalePreamble())
-    Result.UsedBytes += Preamble->Preamble.getSize();
+    Result.UsedBytesPreamble = Preamble->Preamble.getSize();
   return Result;
 }
 
@@ -1429,5 +1443,17 @@
   return P;
 }
 
+MemoryTree TUScheduler::getMemoryUsage() const {
+  MemoryTree MT;
+  MT.addChild("ast_cahe", IdleASTs->getMemoryUsage(), true);
+  // Otherwise preambles are stored on disk and we only keep filename in memory.
+  if (Opts.StorePreamblesInMemory) {
+    MemoryTree Preambles;
+    for (const auto &Elem : fileStats())
+      Preambles.addChild(Elem.first(), Elem.second.UsedBytesPreamble);
+    MT.addChild("preambles", std::move(Preambles), true);
+  }
+  return MT;
+}
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/unittests/ClangdTests.cpp b/clang-tools-extra/clangd/unittests/ClangdTests.cpp
--- a/clang-tools-extra/clangd/unittests/ClangdTests.cpp
+++ b/clang-tools-extra/clangd/unittests/ClangdTests.cpp
@@ -565,7 +565,9 @@
 }
 
 MATCHER_P4(Stats, Name, UsesMemory, PreambleBuilds, ASTBuilds, "") {
-  return arg.first() == Name && (arg.second.UsedBytes != 0) == UsesMemory &&
+  return arg.first() == Name &&
+         (arg.second.UsedBytesAST + arg.second.UsedBytesPreamble != 0) ==
+             UsesMemory &&
          std::tie(arg.second.PreambleBuilds, ASTBuilds) ==
              std::tie(PreambleBuilds, ASTBuilds);
 }