diff --git a/lld/ELF/Driver.h b/lld/ELF/Driver.h
--- a/lld/ELF/Driver.h
+++ b/lld/ELF/Driver.h
@@ -34,7 +34,7 @@
   void createFiles(llvm::opt::InputArgList &args);
   void inferMachineType();
   template <class ELFT> void link(llvm::opt::InputArgList &args);
-  template <class ELFT> void compileBitcodeFiles();
+  template <class ELFT> void compileBitcodeFiles(bool skipLinkedOutput);
 
   // True if we are in --whole-archive and --no-whole-archive.
   bool inWholeArchive = false;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -87,6 +87,7 @@
 
     inputSections.clear();
     outputSections.clear();
+    memoryBuffers.clear();
     archiveFiles.clear();
     binaryFiles.clear();
     bitcodeFiles.clear();
@@ -1994,13 +1995,26 @@
 // using LLVM functions and replaces bitcode symbols with the results.
 // Because all bitcode files that the program consists of are passed to
 // the compiler at once, it can do a whole-program optimization.
-template <class ELFT> void LinkerDriver::compileBitcodeFiles() {
+template <class ELFT>
+void LinkerDriver::compileBitcodeFiles(bool skipLinkedOutput) {
   llvm::TimeTraceScope timeScope("LTO");
   // Compile bitcode files and replace bitcode symbols.
   lto.reset(new BitcodeCompiler);
   for (BitcodeFile *file : bitcodeFiles)
     lto->add(*file);
 
+  // For --thinlto-index-only and other conditions which we skip the normal
+  // linked output, symbol and section names are nearly unused from now on
+  // (except few places like parseSymbolVersion below). Mark input files as
+  // MADV_DONTNEED so that these pages can be reused by the expensive thin link,
+  // saving memory.
+  //
+  // Marking most sections (except .strtab/.shstrtab) as MADV_DONTNEED will save
+  // more memory, but is tricky to implement. So we use this simple approach.
+  if (skipLinkedOutput)
+    for (MemoryBuffer &mb : llvm::make_pointee_range(memoryBuffers))
+      mb.dontNeedIfMmap();
+
   for (InputFile *file : lto->compile()) {
     auto *obj = cast<ObjFile<ELFT>>(file);
     obj->parse(/*ignoreComdats=*/true);
@@ -2364,18 +2378,6 @@
     symtab->scanVersionScript();
   }
 
-  // Do link-time optimization if given files are LLVM bitcode files.
-  // This compiles bitcode files into real object files.
-  //
-  // With this the symbol table should be complete. After this, no new names
-  // except a few linker-synthesized ones will be added to the symbol table.
-  compileBitcodeFiles<ELFT>();
-
-  // Symbol resolution finished. Report backward reference problems.
-  reportBackrefs();
-  if (errorCount())
-    return;
-
   // If --thinlto-index-only is given, we should create only "index
   // files" and not object files. Index file creation is already done
   // in compileBitcodeFiles, so we are done if that's the case.
@@ -2384,8 +2386,23 @@
   // respectively. No object files are generated.
   // Also bail out here when only certain thinLTO modules are specified for
   // compilation. The intermediate object file are the expected output.
-  if (config->thinLTOIndexOnly || config->emitLLVM || config->ltoEmitAsm ||
-      !config->thinLTOModulesToCompile.empty())
+  const bool skipLinkedOutput = config->thinLTOIndexOnly || config->emitLLVM ||
+                                config->ltoEmitAsm ||
+                                !config->thinLTOModulesToCompile.empty();
+
+  // Do link-time optimization if given files are LLVM bitcode files.
+  // This compiles bitcode files into real object files.
+  //
+  // With this the symbol table should be complete. After this, no new names
+  // except a few linker-synthesized ones will be added to the symbol table.
+  compileBitcodeFiles<ELFT>(skipLinkedOutput);
+
+  // Symbol resolution finished. Report backward reference problems.
+  reportBackrefs();
+  if (errorCount())
+    return;
+
+  if (skipLinkedOutput)
     return;
 
   // Handle --exclude-libs again because lto.tmp may reference additional
diff --git a/lld/ELF/InputFiles.h b/lld/ELF/InputFiles.h
--- a/lld/ELF/InputFiles.h
+++ b/lld/ELF/InputFiles.h
@@ -407,6 +407,7 @@
 
 std::string replaceThinLTOSuffix(StringRef path);
 
+extern SmallVector<std::unique_ptr<MemoryBuffer>> memoryBuffers;
 extern SmallVector<ArchiveFile *, 0> archiveFiles;
 extern SmallVector<BinaryFile *, 0> binaryFiles;
 extern SmallVector<BitcodeFile *, 0> bitcodeFiles;
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -43,6 +43,7 @@
 bool InputFile::isInGroup;
 uint32_t InputFile::nextGroupId;
 
+SmallVector<std::unique_ptr<MemoryBuffer>> elf::memoryBuffers;
 SmallVector<ArchiveFile *, 0> elf::archiveFiles;
 SmallVector<BinaryFile *, 0> elf::binaryFiles;
 SmallVector<BitcodeFile *, 0> elf::bitcodeFiles;
@@ -122,9 +123,8 @@
     return None;
   }
 
-  std::unique_ptr<MemoryBuffer> &mb = *mbOrErr;
-  MemoryBufferRef mbref = mb->getMemBufferRef();
-  make<std::unique_ptr<MemoryBuffer>>(std::move(mb)); // take MB ownership
+  MemoryBufferRef mbref = (*mbOrErr)->getMemBufferRef();
+  memoryBuffers.push_back(std::move(*mbOrErr)); // take MB ownership
 
   if (tar)
     tar->append(relativeToRoot(path), mbref.getBuffer());