diff --git a/llvm/lib/ExecutionEngine/Orc/MapperJITLinkMemoryManager.cpp b/llvm/lib/ExecutionEngine/Orc/MapperJITLinkMemoryManager.cpp
--- a/llvm/lib/ExecutionEngine/Orc/MapperJITLinkMemoryManager.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/MapperJITLinkMemoryManager.cpp
@@ -12,8 +12,6 @@
 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
 #include "llvm/Support/Process.h"
 
-#include <limits>
-
 using namespace llvm::jitlink;
 
 namespace llvm {
@@ -34,7 +32,8 @@
     std::swap(AI.Segments, Segs);
     std::swap(AI.Actions, G.allocActions());
 
-    Parent.Mapper->initialize(AI, [&](Expected<ExecutorAddr> Result) {
+    Parent.Mapper->initialize(AI, [OnFinalize = std::move(OnFinalize)](
+                                      Expected<ExecutorAddr> Result) mutable {
       if (!Result) {
         OnFinalize(Result.takeError());
         return;
diff --git a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
--- a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
@@ -11,6 +11,8 @@
 #include "llvm/ExecutionEngine/Orc/Shared/OrcRTBridge.h"
 #include "llvm/Support/WindowsError.h"
 
+#include <algorithm>
+
 #if defined(LLVM_ON_UNIX) && !defined(__ANDROID__)
 #include <fcntl.h>
 #include <sys/mman.h>
@@ -300,9 +302,10 @@
 
 void SharedMemoryMapper::initialize(MemoryMapper::AllocInfo &AI,
                                     OnInitializedFunction OnInitialized) {
-  auto Reservation = Reservations.find(AI.MappingBase);
-  assert(Reservation != Reservations.end() &&
-         "Attempt to initialize unreserved range");
+  auto Reservation = std::lower_bound(
+      Reservations.rbegin(), Reservations.rend(), AI.MappingBase,
+      [](const auto &A, const auto &B) { return A.first > B; });
+  assert(Reservation != Reservations.rend() && "Attempt to initialize unreserved range");
 
   tpctypes::SharedMemoryFinalizeRequest FR;
 
@@ -336,7 +339,7 @@
 
         OnInitialized(std::move(Result));
       },
-      SAs.Instance, AI.MappingBase, std::move(FR));
+      SAs.Instance, Reservation->first, std::move(FR));
 }
 
 void SharedMemoryMapper::deinitialize(
@@ -407,23 +410,19 @@
 }
 
 SharedMemoryMapper::~SharedMemoryMapper() {
-  std::vector<ExecutorAddr> ReservationAddrs;
-  if (!Reservations.empty()) {
-    std::lock_guard<std::mutex> Lock(Mutex);
-    {
-      ReservationAddrs.reserve(Reservations.size());
-      for (const auto &R : Reservations) {
-        ReservationAddrs.push_back(R.first);
-      }
-    }
-  }
+  for (const auto R : Reservations) {
 
-  std::promise<MSVCPError> P;
-  auto F = P.get_future();
-  release(ReservationAddrs, [&](Error Err) { P.set_value(std::move(Err)); });
-  // FIXME: Release can actually fail. The error should be propagated.
-  // Meanwhile, a better option is to explicitly call release().
-  cantFail(F.get());
+#if defined(LLVM_ON_UNIX) && !defined(__ANDROID__)
+
+    munmap(R.second.LocalAddr, R.second.Size);
+
+#elif defined(_WIN32)
+
+  UnmapViewOfFile(R.second.LocalAddr);
+
+#endif
+
+  }
 }
 
 } // namespace orc
diff --git a/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp b/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
--- a/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
@@ -198,6 +198,17 @@
         AllErr = joinErrors(std::move(AllErr), std::move(Err));
       }
 
+      // Remove the allocation from the allocation list of its reservation
+      for (auto &Reservation : Reservations) {
+        auto AllocationIt =
+            std::find(Reservation.second.Allocations.begin(),
+                      Reservation.second.Allocations.end(), Base);
+        if (AllocationIt != Reservation.second.Allocations.end()) {
+          Reservation.second.Allocations.erase(AllocationIt);
+          break;
+        }
+      }
+
       Allocations.erase(Base);
     }
   }
@@ -265,18 +276,13 @@
 
 Error ExecutorSharedMemoryMapperService::shutdown() {
   std::vector<ExecutorAddr> ReservationAddrs;
-  {
-    std::lock_guard<std::mutex> Lock(Mutex);
-
-    if (Reservations.empty())
-      return Error::success();
 
-    ReservationAddrs.reserve(Reservations.size());
-    for (const auto &R : Reservations) {
-      ReservationAddrs.push_back(ExecutorAddr::fromPtr(R.getFirst()));
-    }
+  if (Reservations.empty())
+    return Error::success();
 
-    Reservations.clear();
+  ReservationAddrs.reserve(Reservations.size());
+  for (const auto &R : Reservations) {
+    ReservationAddrs.push_back(ExecutorAddr::fromPtr(R.getFirst()));
   }
 
   return release(ReservationAddrs);