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 profile(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
@@ -16,6 +16,7 @@
 #include "URI.h"
 #include "index/BackgroundIndexLoader.h"
 #include "index/FileIndex.h"
+#include "index/Index.h"
 #include "index/IndexAction.h"
 #include "index/MemIndex.h"
 #include "index/Ref.h"
@@ -414,5 +415,10 @@
   return {TUsToIndex.begin(), TUsToIndex.end()};
 }
 
+void BackgroundIndex::profile(MemoryTree &MT) const {
+  IndexedSymbols.profile(MT.child("symbols"));
+  // We don't want to mix memory used by index and symbols, so call base class.
+  MT.child("index").addUsage(SwapIndex::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 profile(MemoryTree &MT) const;
+
 private:
   struct RefSlabAndCountReferences {
     std::shared_ptr<RefSlab> Slab;
@@ -116,6 +119,8 @@
   /// `indexMainDecls`.
   void updateMain(PathRef Path, ParsedAST &AST);
 
+  void profile(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"
@@ -388,6 +389,25 @@
   llvm_unreachable("Unknown clangd::IndexType");
 }
 
+void FileSymbols::profile(MemoryTree &MT) const {
+  std::lock_guard<std::mutex> Lock(Mutex);
+  for (const auto &SymSlab : SymbolsSnapshot) {
+    MT.detail(SymSlab.first())
+        .child("symbols")
+        .addUsage(SymSlab.second->bytes());
+  }
+  for (const auto &RefSlab : RefsSnapshot) {
+    MT.detail(RefSlab.first())
+        .child("references")
+        .addUsage(RefSlab.second.Slab->bytes());
+  }
+  for (const auto &RelSlab : RelationsSnapshot) {
+    MT.detail(RelSlab.first())
+        .child("relations")
+        .addUsage(RelSlab.second->bytes());
+  }
+}
+
 FileIndex::FileIndex(bool UseDex, bool CollectMainFileRefs)
     : MergedIndex(&MainFileIndex, &PreambleIndex), UseDex(UseDex),
       CollectMainFileRefs(CollectMainFileRefs),
@@ -457,5 +477,15 @@
   }
 }
 
+void FileIndex::profile(MemoryTree &MT) const {
+  PreambleSymbols.profile(MT.child("preamble").child("symbols"));
+  MT.child("preamble")
+      .child("index")
+      .addUsage(PreambleIndex.estimateMemoryUsage());
+  MainFileSymbols.profile(MT.child("main_file").child("symbols"));
+  MT.child("main_file")
+      .child("index")
+      .addUsage(MainFileIndex.estimateMemoryUsage());
+}
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp b/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp
--- a/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp
+++ b/clang-tools-extra/clangd/unittests/BackgroundIndexTests.cpp
@@ -21,6 +21,7 @@
 using ::testing::Contains;
 using ::testing::ElementsAre;
 using ::testing::Not;
+using ::testing::Pair;
 using ::testing::UnorderedElementsAre;
 
 namespace clang {
@@ -916,5 +917,18 @@
   EXPECT_EQ(S.LastIdle, 2000u);
 }
 
+TEST(BackgroundIndex, Profile) {
+  MockFS FS;
+  MockCompilationDatabase CDB;
+  BackgroundIndex Idx(FS, CDB, [](llvm::StringRef) { return nullptr; },
+                      /*Opts=*/{});
+
+  llvm::BumpPtrAllocator Alloc;
+  MemoryTree MT(&Alloc);
+  Idx.profile(MT);
+  ASSERT_THAT(MT.children(),
+              UnorderedElementsAre(Pair("symbols", _), Pair("index", _)));
+}
+
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/unittests/FileIndexTests.cpp b/clang-tools-extra/clangd/unittests/FileIndexTests.cpp
--- a/clang-tools-extra/clangd/unittests/FileIndexTests.cpp
+++ b/clang-tools-extra/clangd/unittests/FileIndexTests.cpp
@@ -22,20 +22,25 @@
 #include "index/Relation.h"
 #include "index/Serialization.h"
 #include "index/Symbol.h"
+#include "index/SymbolID.h"
 #include "support/Threading.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/Utils.h"
 #include "clang/Index/IndexSymbol.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/CompilationDatabase.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/Allocator.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <utility>
+#include <vector>
 
 using ::testing::_;
 using ::testing::AllOf;
 using ::testing::Contains;
 using ::testing::ElementsAre;
+using ::testing::Gt;
 using ::testing::IsEmpty;
 using ::testing::Pair;
 using ::testing::UnorderedElementsAre;
@@ -88,6 +93,13 @@
   return std::make_unique<RefSlab>(std::move(Slab).build());
 }
 
+std::unique_ptr<RelationSlab> relSlab(llvm::ArrayRef<const Relation> Rels) {
+  RelationSlab::Builder RelBuilder;
+  for (auto &Rel : Rels)
+    RelBuilder.insert(Rel);
+  return std::make_unique<RelationSlab>(std::move(RelBuilder).build());
+}
+
 TEST(FileSymbolsTest, UpdateAndGet) {
   FileSymbols FS;
   EXPECT_THAT(runFuzzyFind(*FS.buildIndex(IndexType::Light), ""), IsEmpty());
@@ -643,6 +655,50 @@
     EXPECT_TRUE(Shard->Cmd.hasValue());
   }
 }
+
+TEST(FileIndexTest, Profile) {
+  FileIndex FI;
+
+  auto FileName = testPath("foo.cpp");
+  auto AST = TestTU::withHeaderCode("int a;").build();
+  FI.updateMain(FileName, AST);
+  FI.updatePreamble(FileName, "v1", AST.getASTContext(),
+                    AST.getPreprocessorPtr(), AST.getCanonicalIncludes());
+
+  llvm::BumpPtrAllocator Alloc;
+  MemoryTree MT(&Alloc);
+  FI.profile(MT);
+  ASSERT_THAT(MT.children(),
+              UnorderedElementsAre(Pair("preamble", _), Pair("main_file", _)));
+
+  ASSERT_THAT(MT.child("preamble").children(),
+              UnorderedElementsAre(Pair("index", _), Pair("symbols", _)));
+  ASSERT_THAT(MT.child("main_file").children(),
+              UnorderedElementsAre(Pair("index", _), Pair("symbols", _)));
+
+  ASSERT_THAT(MT.child("preamble").child("index").total(), Gt(0U));
+  ASSERT_THAT(MT.child("main_file").child("index").total(), Gt(0U));
+}
+
+TEST(FileSymbolsTest, Profile) {
+  FileSymbols FS;
+  FS.update("f1", numSlab(1, 2), nullptr, nullptr, false);
+  FS.update("f2", nullptr, refSlab(SymbolID("1"), "f1"), nullptr, false);
+  FS.update("f3", nullptr, nullptr,
+            relSlab({{SymbolID("1"), RelationKind::BaseOf, SymbolID("2")}}),
+            false);
+  llvm::BumpPtrAllocator Alloc;
+  MemoryTree MT(&Alloc);
+  FS.profile(MT);
+  ASSERT_THAT(MT.children(), UnorderedElementsAre(Pair("f1", _), Pair("f2", _),
+                                                  Pair("f3", _)));
+  EXPECT_THAT(MT.child("f1").children(), ElementsAre(Pair("symbols", _)));
+  EXPECT_THAT(MT.child("f1").total(), Gt(0U));
+  EXPECT_THAT(MT.child("f2").children(), ElementsAre(Pair("references", _)));
+  EXPECT_THAT(MT.child("f2").total(), Gt(0U));
+  EXPECT_THAT(MT.child("f3").children(), ElementsAre(Pair("relations", _)));
+  EXPECT_THAT(MT.child("f3").total(), Gt(0U));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang