diff --git a/clang-tools-extra/clangd/index/Background.h b/clang-tools-extra/clangd/index/Background.h
--- a/clang-tools-extra/clangd/index/Background.h
+++ b/clang-tools-extra/clangd/index/Background.h
@@ -16,9 +16,11 @@
 #include "index/Index.h"
 #include "index/Serialization.h"
 #include "support/Context.h"
+#include "support/MemoryTree.h"
 #include "support/Path.h"
 #include "support/Threading.h"
 #include "support/ThreadsafeFS.h"
+#include "support/Trace.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/Threading.h"
@@ -172,6 +174,8 @@
     return Queue.blockUntilIdleForTest(TimeoutSeconds);
   }
 
+  void attachMemoryUsage(MemoryTree &MT) const;
+
 private:
   /// Represents the state of a single file when indexing was performed.
   struct ShardVersion {
diff --git a/clang-tools-extra/clangd/index/Background.cpp b/clang-tools-extra/clangd/index/Background.cpp
--- a/clang-tools-extra/clangd/index/Background.cpp
+++ b/clang-tools-extra/clangd/index/Background.cpp
@@ -414,5 +414,9 @@
   return {TUsToIndex.begin(), TUsToIndex.end()};
 }
 
+void BackgroundIndex::attachMemoryUsage(MemoryTree &MT) const {
+  IndexedSymbols.attachMemoryUsage(*MT.addChild("symbols"));
+  MT.addChild("index")->addUsage(estimateMemoryUsage());
+}
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/index/FileIndex.h b/clang-tools-extra/clangd/index/FileIndex.h
--- a/clang-tools-extra/clangd/index/FileIndex.h
+++ b/clang-tools-extra/clangd/index/FileIndex.h
@@ -24,6 +24,7 @@
 #include "index/Relation.h"
 #include "index/Serialization.h"
 #include "index/Symbol.h"
+#include "support/MemoryTree.h"
 #include "support/Path.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/CompilationDatabase.h"
@@ -87,6 +88,8 @@
              DuplicateHandling DuplicateHandle = DuplicateHandling::PickOne,
              size_t *Version = nullptr);
 
+  void attachMemoryUsage(MemoryTree &MT) const;
+
 private:
   struct RefSlabAndCountReferences {
     std::shared_ptr<RefSlab> Slab;
@@ -116,6 +119,8 @@
   /// `indexMainDecls`.
   void updateMain(PathRef Path, ParsedAST &AST);
 
+  void attachMemoryUsage(MemoryTree &MT) const;
+
 private:
   bool UseDex; // FIXME: this should be always on.
   bool CollectMainFileRefs;
diff --git a/clang-tools-extra/clangd/index/FileIndex.cpp b/clang-tools-extra/clangd/index/FileIndex.cpp
--- a/clang-tools-extra/clangd/index/FileIndex.cpp
+++ b/clang-tools-extra/clangd/index/FileIndex.cpp
@@ -22,6 +22,7 @@
 #include "index/SymbolOrigin.h"
 #include "index/dex/Dex.h"
 #include "support/Logger.h"
+#include "support/MemoryTree.h"
 #include "support/Path.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/Index/IndexingAction.h"
@@ -373,6 +374,16 @@
   llvm_unreachable("Unknown clangd::IndexType");
 }
 
+void FileSymbols::attachMemoryUsage(MemoryTree &MT) const {
+  std::lock_guard<std::mutex> Lock(Mutex);
+  for (const auto &SymSlab : SymbolsSnapshot)
+    MT.addDetail(SymSlab.first())->addUsage(SymSlab.second->bytes());
+  for (const auto &RefSlab : RefsSnapshot)
+    MT.addDetail(RefSlab.first())->addUsage(RefSlab.second.Slab->bytes());
+  for (const auto &RelSlab : SymbolsSnapshot)
+    MT.addDetail(RelSlab.first())->addUsage(RelSlab.second->bytes());
+}
+
 FileIndex::FileIndex(bool UseDex, bool CollectMainFileRefs)
     : MergedIndex(&MainFileIndex, &PreambleIndex), UseDex(UseDex),
       CollectMainFileRefs(CollectMainFileRefs),
@@ -442,5 +453,11 @@
   }
 }
 
+void FileIndex::attachMemoryUsage(MemoryTree &MT) const {
+  PreambleSymbols.attachMemoryUsage(*MT.addChild("preamble_symbols"));
+  MT.addChild("preamble_index")->addUsage(PreambleIndex.estimateMemoryUsage());
+  MainFileSymbols.attachMemoryUsage(*MT.addChild("main_file_symbols"));
+  MT.addChild("main_file_index")->addUsage(MainFileIndex.estimateMemoryUsage());
+}
 } // namespace clangd
 } // namespace clang