diff --git a/mmtk/Cargo.lock b/mmtk/Cargo.lock
index c8d073e8..be0729cf 100644
--- a/mmtk/Cargo.lock
+++ b/mmtk/Cargo.lock
@@ -449,7 +449,7 @@ dependencies = [
 [[package]]
 name = "mmtk"
 version = "0.22.1"
-source = "git+https://github.com/mmtk/mmtk-core.git?rev=ef2bd6d043d8675badaa415db89be7b52439725f#ef2bd6d043d8675badaa415db89be7b52439725f"
+source = "git+https://github.com/mmtk/mmtk-core.git?rev=7cafe560139211c0e3a74815d2e288278506099d#7cafe560139211c0e3a74815d2e288278506099d"
 dependencies = [
  "atomic 0.6.0",
  "atomic-traits",
@@ -500,7 +500,7 @@ dependencies = [
 [[package]]
 name = "mmtk-macros"
 version = "0.22.1"
-source = "git+https://github.com/mmtk/mmtk-core.git?rev=ef2bd6d043d8675badaa415db89be7b52439725f#ef2bd6d043d8675badaa415db89be7b52439725f"
+source = "git+https://github.com/mmtk/mmtk-core.git?rev=7cafe560139211c0e3a74815d2e288278506099d#7cafe560139211c0e3a74815d2e288278506099d"
 dependencies = [
  "proc-macro-error",
  "proc-macro2",
diff --git a/mmtk/Cargo.toml b/mmtk/Cargo.toml
index 9c1d1287..fe5fac16 100644
--- a/mmtk/Cargo.toml
+++ b/mmtk/Cargo.toml
@@ -10,7 +10,7 @@ edition = "2018"
 [package.metadata.julia]
 # Our CI matches the following line and extract mmtk/julia. If this line is updated, please check ci yaml files and make sure it works.
 julia_repo = "https://github.com/mmtk/julia.git"
-julia_version = "5c406d9bb20d76e2298a6101f171cfac491f651c"
+julia_version = "22524a81f9920a8ecc70f195d53b145761de2fa0"
 
 [lib]
 crate-type = ["cdylib"]
@@ -31,7 +31,7 @@ lazy_static = "1.1"
 # - change branch
 # - change repo name
 # But other changes including adding/removing whitespaces in commented lines may break the CI
-mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev="ef2bd6d043d8675badaa415db89be7b52439725f" }
+mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev="7cafe560139211c0e3a74815d2e288278506099d" }
 # Uncomment the following to build locally
 # mmtk = { path = "../repos/mmtk-core" }
 log = {version = "0.4", features = ["max_level_trace", "release_max_level_off"] }
diff --git a/mmtk/api/mmtk.h b/mmtk/api/mmtk.h
index e3d10c4a..9ddd411b 100644
--- a/mmtk/api/mmtk.h
+++ b/mmtk/api/mmtk.h
@@ -95,8 +95,6 @@ extern bool mmtk_process(char* name, char* value);
 extern void mmtk_scan_region(void);
 extern void mmtk_handle_user_collection_request(void *tls, uint8_t collection);
 extern void mmtk_initialize_collection(void* tls);
-extern void mmtk_enable_collection(void);
-extern void mmtk_disable_collection(void);
 extern void mmtk_start_control_collector(void *tls);
 extern void mmtk_start_worker(void *tls, void* worker, void* mmtk);
 extern void mmtk_process_julia_obj(void* addr);
diff --git a/mmtk/src/api.rs b/mmtk/src/api.rs
index 0e647ed2..a8eaa11a 100644
--- a/mmtk/src/api.rs
+++ b/mmtk/src/api.rs
@@ -3,7 +3,6 @@
 
 use crate::JuliaVM;
 use crate::Julia_Upcalls;
-use crate::BLOCK_FOR_GC;
 use crate::JULIA_HEADER_SIZE;
 use crate::SINGLETON;
 use crate::UPCALLS;
@@ -240,30 +239,6 @@ pub extern "C" fn mmtk_initialize_collection(tls: VMThread) {
     memory_manager::initialize_collection(&SINGLETON, tls);
 }
 
-#[no_mangle]
-pub extern "C" fn mmtk_enable_collection() {
-    if AtomicBool::load(&DISABLED_GC, Ordering::SeqCst) {
-        memory_manager::enable_collection(&SINGLETON);
-        AtomicBool::store(&DISABLED_GC, false, Ordering::SeqCst);
-    }
-}
-
-#[no_mangle]
-pub extern "C" fn mmtk_disable_collection() {
-    if AtomicBool::load(&DISABLED_GC, Ordering::SeqCst) == false {
-        AtomicBool::store(&DISABLED_GC, true, Ordering::SeqCst);
-        memory_manager::disable_collection(&SINGLETON);
-    }
-
-    // if user has triggered GC, wait until GC is finished
-    while AtomicIsize::load(&USER_TRIGGERED_GC, Ordering::SeqCst) != 0
-        || AtomicBool::load(&BLOCK_FOR_GC, Ordering::SeqCst)
-    {
-        info!("Waiting for a triggered gc to finish...");
-        unsafe { ((*UPCALLS).wait_in_a_safepoint)() };
-    }
-}
-
 #[no_mangle]
 pub extern "C" fn mmtk_used_bytes() -> usize {
     memory_manager::used_bytes(&SINGLETON)
diff --git a/mmtk/src/collection.rs b/mmtk/src/collection.rs
index a2c30c14..230f74cb 100644
--- a/mmtk/src/collection.rs
+++ b/mmtk/src/collection.rs
@@ -5,12 +5,16 @@ use mmtk::util::alloc::AllocationError;
 use mmtk::util::opaque_pointer::*;
 use mmtk::vm::{Collection, GCThreadContext};
 use mmtk::Mutator;
-use std::sync::atomic::{AtomicBool, AtomicIsize, AtomicU64, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicIsize, AtomicU32, AtomicU64, Ordering};
 
 use crate::{BLOCK_FOR_GC, STW_COND, WORLD_HAS_STOPPED};
 
 static GC_START: AtomicU64 = AtomicU64::new(0);
 
+extern "C" {
+    pub static jl_gc_disable_counter: AtomicU32;
+}
+
 pub struct VMCollection {}
 
 impl Collection<JuliaVM> for VMCollection {
@@ -100,6 +104,10 @@ impl Collection<JuliaVM> for VMCollection {
     fn vm_live_bytes() -> usize {
         crate::api::JULIA_MALLOC_BYTES.load(Ordering::SeqCst)
     }
+
+    fn is_collection_enabled() -> bool {
+        unsafe { AtomicU32::load(&jl_gc_disable_counter, Ordering::SeqCst) <= 0 }
+    }
 }
 
 pub fn is_current_gc_nursery() -> bool {