diff --git a/Make.inc b/Make.inc
index 5a0d97ac4843d..c6474cf0a377b 100644
--- a/Make.inc
+++ b/Make.inc
@@ -767,6 +767,10 @@ ifeq (${MMTK_PLAN},StickyImmix)
 JCXXFLAGS += -DMMTK_PLAN_STICKYIMMIX
 JCFLAGS += -DMMTK_PLAN_STICKYIMMIX
 endif
+ifeq (${MMTK_CONSERVATIVE},1)
+JCXXFLAGS += -DMMTK_CONSERVATIVE_SCAN
+JCFLAGS += -DMMTK_CONSERVATIVE_SCAN
+endif
 MMTK_DIR = ${MMTK_JULIA_DIR}/mmtk
 MMTK_API_INC = $(MMTK_DIR)/api
 MMTK_JULIA_INC = ${MMTK_JULIA_DIR}/julia
diff --git a/src/datatype.c b/src/datatype.c
index 345bab270e912..8667d245462ad 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -276,6 +276,10 @@ static jl_datatype_layout_t *jl_get_layout(uint32_t sz,
     if ((void*)ret == HT_NOTFOUND) {
         if (!should_malloc) {
             char *perm_mem = (char *)jl_gc_perm_alloc(flddesc_sz, 0, 4, 0);
+#ifdef MMTK_GC
+            jl_ptls_t ptls = jl_current_task->ptls;
+            mmtk_immortal_post_alloc_fast(&ptls->mmtk_mutator, jl_valueof(perm_mem), flddesc_sz);
+#endif
             assert(perm_mem);
             ret = (jl_datatype_layout_t *)perm_mem;
             memcpy(perm_mem, flddesc, flddesc_sz);
@@ -815,6 +819,10 @@ JL_DLLEXPORT jl_datatype_t * jl_new_foreign_type(jl_sym_t *name,
     jl_datatype_layout_t *layout = (jl_datatype_layout_t *)
       jl_gc_perm_alloc(sizeof(jl_datatype_layout_t) + sizeof(jl_fielddescdyn_t),
         0, 4, 0);
+#ifdef MMTK_GC
+    jl_ptls_t ptls = jl_current_task->ptls;
+    mmtk_immortal_post_alloc_fast(&ptls->mmtk_mutator, jl_valueof(layout), sizeof(jl_datatype_layout_t) + sizeof(jl_fielddescdyn_t));
+#endif
     layout->size = large ? GC_MAX_SZCLASS+1 : 0;
     layout->nfields = 0;
     layout->alignment = sizeof(void *);
diff --git a/src/gc.c b/src/gc.c
index 74a720260e7d5..03c309716110e 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -3578,6 +3578,11 @@ JL_DLLEXPORT jl_value_t *jl_gc_internal_obj_base_ptr(void *p)
     return NULL;
 }
 
+JL_DLLEXPORT void jl_gc_post_alloc_slow(void* obj, int size) JL_NOTSAFEPOINT
+{
+    jl_unreachable();
+}
+
 JL_DLLEXPORT void jl_gc_wb1_noinline(const void *parent) JL_NOTSAFEPOINT
 {
     jl_unreachable();
diff --git a/src/jl_exported_funcs.inc b/src/jl_exported_funcs.inc
index 54699ca46c78f..292c71ab54b2e 100644
--- a/src/jl_exported_funcs.inc
+++ b/src/jl_exported_funcs.inc
@@ -198,6 +198,7 @@
     XX(jl_gc_wb_binding_noinline) \
     XX(jl_gc_wb1_slow) \
     XX(jl_gc_wb2_slow) \
+    XX(jl_gc_post_alloc_slow) \
     XX(jl_gc_safepoint) \
     XX(jl_gc_schedule_foreign_sweepfunc) \
     XX(jl_gc_set_cb_notify_external_alloc) \
diff --git a/src/julia.h b/src/julia.h
index b23f2bc561502..acc78d5a0c74c 100644
--- a/src/julia.h
+++ b/src/julia.h
@@ -2438,8 +2438,11 @@ extern JL_DLLEXPORT int jl_default_debug_info_kind;
 extern void mmtk_object_reference_write_post(void* mutator, const void* parent, const void* ptr);
 extern void mmtk_object_reference_write_slow(void* mutator, const void* parent, const void* ptr);
 extern void* mmtk_alloc(void* mutator, size_t size, size_t align, size_t offset, int allocator);
+extern void mmtk_post_alloc(void* mutator, void* refer, size_t bytes, int allocator);
+
 
 extern const void* MMTK_SIDE_LOG_BIT_BASE_ADDRESS;
+extern const void* MMTK_SIDE_VO_BIT_BASE_ADDRESS;
 
 // These need to be constants.
 
@@ -2452,6 +2455,12 @@ extern const void* MMTK_SIDE_LOG_BIT_BASE_ADDRESS;
 #define MMTK_NEEDS_WRITE_BARRIER (1)
 #endif
 
+#ifdef MMTK_CONSERVATIVE_SCAN
+#define MMTK_NEEDS_VO_BIT (1)
+#else
+#define MMTK_NEEDS_VO_BIT (0)
+#endif
+
 #define MMTK_DEFAULT_IMMIX_ALLOCATOR (0)
 #define MMTK_IMMORTAL_BUMP_ALLOCATOR (0)
 
@@ -2526,8 +2535,23 @@ STATIC_INLINE void* mmtk_immix_alloc_fast(MMTkMutatorContext* mutator, size_t si
     return bump_alloc_fast(mutator, (uintptr_t*)&allocator->cursor, (intptr_t)allocator->limit, size, align, offset, 0);
 }
 
+STATIC_INLINE void mmtk_immix_post_alloc_slow(MMTkMutatorContext* mutator, void* obj, size_t size) {
+    mmtk_post_alloc(mutator, obj, size, 0);
+}
+
+STATIC_INLINE void mmtk_set_vo_bit(void* obj) {
+        intptr_t addr = (intptr_t) obj;
+        intptr_t shift = (addr >> 3) & 0b111;
+        uint8_t* vo_meta_addr = (uint8_t*) (MMTK_SIDE_VO_BIT_BASE_ADDRESS) + (addr >> 6);
+        uint8_t new_val = (*vo_meta_addr) | (1 << shift);
+        (*vo_meta_addr) = new_val;
+}
+
 STATIC_INLINE void mmtk_immix_post_alloc_fast(MMTkMutatorContext* mutator, void* obj, size_t size) {
-    // We do not need post alloc for immix objects in immix/stickyimmix
+    if (MMTK_NEEDS_VO_BIT) {
+        // set VO bit
+        mmtk_set_vo_bit(obj);
+    }
 }
 
 STATIC_INLINE void* mmtk_immortal_alloc_fast(MMTkMutatorContext* mutator, size_t size, size_t align, size_t offset) {
@@ -2536,10 +2560,15 @@ STATIC_INLINE void* mmtk_immortal_alloc_fast(MMTkMutatorContext* mutator, size_t
 }
 
 STATIC_INLINE void mmtk_immortal_post_alloc_fast(MMTkMutatorContext* mutator, void* obj, size_t size) {
+    if (MMTK_NEEDS_VO_BIT) {
+        // set VO bit
+        mmtk_set_vo_bit(obj);
+    }
+
     if (MMTK_NEEDS_WRITE_BARRIER == MMTK_OBJECT_BARRIER) {
         intptr_t addr = (intptr_t) obj;
-        uint8_t* meta_addr = (uint8_t*) (MMTK_SIDE_LOG_BIT_BASE_ADDRESS) + (addr >> 6);
         intptr_t shift = (addr >> 3) & 0b111;
+        uint8_t* meta_addr = (uint8_t*) (MMTK_SIDE_LOG_BIT_BASE_ADDRESS) + (addr >> 6);
         while(1) {
             uint8_t old_val = *meta_addr;
             uint8_t new_val = old_val | (1 << shift);
diff --git a/src/llvm-final-gc-lowering.cpp b/src/llvm-final-gc-lowering.cpp
index 74e69d9d6fa9f..02be0ac3e1922 100644
--- a/src/llvm-final-gc-lowering.cpp
+++ b/src/llvm-final-gc-lowering.cpp
@@ -59,6 +59,7 @@ struct FinalLowerGC: private JuliaPassContext {
     Function *writeBarrierBindingFunc;
     Function *writeBarrier1SlowFunc;
     Function *writeBarrier2SlowFunc;
+    Function *postAllocSlowFunc;
 #endif
     Instruction *pgcstack;
 
@@ -373,6 +374,45 @@ Value *FinalLowerGC::lowerGCAllocBytes(CallInst *target, Function &F)
 
                 auto v_raw = builder.CreateNSWAdd(result, ConstantInt::get(Type::getInt64Ty(target->getContext()), sizeof(jl_taggedvalue_t)));
                 auto v_as_ptr = builder.CreateIntToPtr(v_raw, poolAllocFunc->getReturnType());
+
+                if (MMTK_NEEDS_VO_BIT) {
+                    // Should we generate fastpath post alloc sequence here?
+                    // Setting this to false will increase allocation overhead a lot, and should only be used for debugging.
+                    const bool INLINE_FASTPATH_POST_ALLOCATION = true;
+
+                    // set VO bit
+                    if (INLINE_FASTPATH_POST_ALLOCATION) {
+                        auto intptr_ty = Type::getInt64Ty(target->getContext());
+                        auto i8_ty = Type::getInt8Ty(F.getContext());
+                        intptr_t metadata_base_address = reinterpret_cast<intptr_t>(MMTK_SIDE_VO_BIT_BASE_ADDRESS);
+                        auto metadata_base_val = ConstantInt::get(intptr_ty, metadata_base_address);
+                        auto metadata_base_ptr = ConstantExpr::getIntToPtr(metadata_base_val, PointerType::get(i8_ty, 0));
+
+                        // intptr_t addr = (intptr_t) v;
+                        auto addr = v_raw;
+
+                        // uint8_t* vo_meta_addr = (uint8_t*) (MMTK_SIDE_VO_BIT_BASE_ADDRESS) + (addr >> 6);
+                        auto shr = builder.CreateLShr(addr, ConstantInt::get(intptr_ty, 6));
+                        auto metadata_ptr = builder.CreateGEP(i8_ty, metadata_base_ptr, shr);
+
+                        // intptr_t shift = (addr >> 3) & 0b111;
+                        auto shift = builder.CreateAnd(builder.CreateLShr(addr, ConstantInt::get(intptr_ty, 3)), ConstantInt::get(intptr_ty, 7));
+
+                        // uint8_t byte_val = *vo_meta_addr;
+                        auto byte_val = builder.CreateAlignedLoad(i8_ty, metadata_ptr, Align());
+
+                        // uint8_t new_val = byte_val | (1 << shift);
+                        auto shifted_val = builder.CreateShl(ConstantInt::get(intptr_ty, 1), shift);
+                        auto shifted_val_i8 = builder.CreateTruncOrBitCast(shifted_val, i8_ty);
+                        auto new_val = builder.CreateOr(byte_val, shifted_val_i8);
+
+                        // (*vo_meta_addr) = new_val;
+                        builder.CreateStore(new_val, metadata_ptr);
+                    } else {
+                        builder.CreateCall(postAllocSlowFunc, { v_as_ptr, pool_osize_i32 });
+                    }
+                }
+
                 builder.CreateBr(top_cont);
 
                 phiNode->addIncoming(new_call, slowpath);
@@ -416,7 +456,8 @@ bool FinalLowerGC::doInitialization(Module &M) {
     writeBarrierBindingFunc = getOrDeclare(jl_well_known::GCWriteBarrierBinding);
     writeBarrier1SlowFunc = getOrDeclare(jl_well_known::GCWriteBarrier1Slow);
     writeBarrier2SlowFunc = getOrDeclare(jl_well_known::GCWriteBarrier2Slow);
-    GlobalValue *functionList[] = {queueRootFunc, poolAllocFunc, bigAllocFunc, gcPreserveBeginHookFunc, gcPreserveEndHookFunc, writeBarrier1Func, writeBarrier2Func, writeBarrierBindingFunc, writeBarrier1SlowFunc, writeBarrier2SlowFunc};
+    postAllocSlowFunc = getOrDeclare(jl_well_known::GCPostAllocSlow);
+    GlobalValue *functionList[] = {queueRootFunc, poolAllocFunc, bigAllocFunc, gcPreserveBeginHookFunc, gcPreserveEndHookFunc, writeBarrier1Func, writeBarrier2Func, writeBarrierBindingFunc, writeBarrier1SlowFunc, writeBarrier2SlowFunc, postAllocSlowFunc};
 #else
     GlobalValue *functionList[] = {queueRootFunc, queueBindingFunc, poolAllocFunc, bigAllocFunc, allocTypedFunc};
 #endif
@@ -436,8 +477,8 @@ bool FinalLowerGC::doInitialization(Module &M) {
 bool FinalLowerGC::doFinalization(Module &M)
 {
 #ifdef MMTK_GC
-    GlobalValue *functionList[] = {queueRootFunc, poolAllocFunc, bigAllocFunc, gcPreserveBeginHookFunc, gcPreserveEndHookFunc, writeBarrier1Func, writeBarrier2Func, writeBarrierBindingFunc, writeBarrier1SlowFunc, writeBarrier2SlowFunc};
-    queueRootFunc = poolAllocFunc = bigAllocFunc = gcPreserveBeginHookFunc = gcPreserveEndHookFunc = writeBarrier1Func = writeBarrier2Func = writeBarrierBindingFunc = writeBarrier1SlowFunc = writeBarrier2SlowFunc = nullptr;
+    GlobalValue *functionList[] = {queueRootFunc, poolAllocFunc, bigAllocFunc, gcPreserveBeginHookFunc, gcPreserveEndHookFunc, writeBarrier1Func, writeBarrier2Func, writeBarrierBindingFunc, writeBarrier1SlowFunc, writeBarrier2SlowFunc, postAllocSlowFunc};
+    queueRootFunc = poolAllocFunc = bigAllocFunc = gcPreserveBeginHookFunc = gcPreserveEndHookFunc = writeBarrier1Func = writeBarrier2Func = writeBarrierBindingFunc = writeBarrier1SlowFunc = writeBarrier2SlowFunc = postAllocSlowFunc = nullptr;
 #else
     GlobalValue *functionList[] = {queueRootFunc, queueBindingFunc, poolAllocFunc, bigAllocFunc, allocTypedFunc};
     queueRootFunc = queueBindingFunc = poolAllocFunc = bigAllocFunc = allocTypedFunc = nullptr;
diff --git a/src/llvm-pass-helpers.cpp b/src/llvm-pass-helpers.cpp
index 8d2e0c2d14ca5..7f18bc354831b 100644
--- a/src/llvm-pass-helpers.cpp
+++ b/src/llvm-pass-helpers.cpp
@@ -341,6 +341,7 @@ namespace jl_well_known {
     static const char *GC_WB_BINDING_NAME = XSTR(jl_gc_wb_binding_noinline);
     static const char *GC_WB_1_SLOW_NAME = XSTR(jl_gc_wb1_slow);
     static const char *GC_WB_2_SLOW_NAME = XSTR(jl_gc_wb2_slow);
+    static const char *GC_POST_ALLOC_SLOW_NAME = XSTR(jl_gc_post_alloc_slow);
 #endif
 
     static auto T_size_t(const JuliaPassContext &context) {
@@ -528,5 +529,19 @@ namespace jl_well_known {
             func->addFnAttr(Attribute::InaccessibleMemOrArgMemOnly);
             return func;
     });
+
+     const WellKnownFunctionDescription GCPostAllocSlow (
+        GC_POST_ALLOC_SLOW_NAME,
+        [](const JuliaPassContext &context) {
+            auto func = Function::Create(
+                FunctionType::get(
+                    Type::getVoidTy(context.getLLVMContext()),
+                    { context.T_prjlvalue, Type::getInt32Ty(context.getLLVMContext()) },
+                    false),
+                Function::ExternalLinkage,
+                GC_POST_ALLOC_SLOW_NAME);
+            func->addFnAttr(Attribute::InaccessibleMemOrArgMemOnly);
+            return func;
+    });
 #endif
 }
diff --git a/src/llvm-pass-helpers.h b/src/llvm-pass-helpers.h
index 1e672433be596..6c169809a87ee 100644
--- a/src/llvm-pass-helpers.h
+++ b/src/llvm-pass-helpers.h
@@ -177,6 +177,7 @@ namespace jl_well_known {
     extern const WellKnownFunctionDescription GCWriteBarrierBinding;
     extern const WellKnownFunctionDescription GCWriteBarrier1Slow;
     extern const WellKnownFunctionDescription GCWriteBarrier2Slow;
+    extern const WellKnownFunctionDescription GCPostAllocSlow;
 #endif
 }
 
diff --git a/src/mmtk-gc.c b/src/mmtk-gc.c
index e0363c8e70386..d18e61db819fc 100644
--- a/src/mmtk-gc.c
+++ b/src/mmtk-gc.c
@@ -647,6 +647,12 @@ JL_DLLEXPORT void jl_gc_wb2_slow(const void *parent, const void* ptr) JL_NOTSAFE
     mmtk_object_reference_write_slow(&ptls->mmtk_mutator, parent, ptr);
 }
 
+JL_DLLEXPORT void jl_gc_post_alloc_slow(void* obj, int size) JL_NOTSAFEPOINT {
+    jl_task_t *ct = jl_current_task;
+    jl_ptls_t ptls = ct->ptls;
+    mmtk_immix_post_alloc_slow(&ptls->mmtk_mutator, obj, size);
+}
+
 void *jl_gc_perm_alloc_nolock(size_t sz, int zero, unsigned align, unsigned offset)
 {
     jl_ptls_t ptls = jl_current_task->ptls;