Switch to pooling copy-on-write instantiation strategy for WASM (#11232)

* Switch to pooling copy-on-write instantiation strategy for WASM

* Fix benchmark compilation

* Fix `cargo fmt`

* Fix compilation of another benchmark I've missed

* Cleanups according to review comments

* Move `max_memory_size` to `Semantics`

* Set `memory_guaranteed_dense_image_size` to `max_memory_size`

* Rename `wasm_instantiation_strategy` to `wasmtime_instantiation_strategy`

* Update the doc-comments regarding the instantiation strategy

* Extend the integration tests to test every instantiation strategy

* Don't drop the temporary directory until the runtime is dropped in benchmarks

* Don't drop the temporary directory until the runtime is dropped in tests

substrate/Cargo.lock

@@ -4173,6 +4173,15 @@ version = "2.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "308cc39be01b73d0d18f82a0e7b2a3df85245f84af96fdddc5d202d27e47b86a"
 
+[[package]]
+name = "memfd"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6627dc657574b49d6ad27105ed671822be56e0d2547d413bfbf3e8d8fa92e7a"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "memmap"
 version = "0.7.0"
@@ -8197,6 +8206,7 @@ dependencies = [
  "hex-literal",
  "lazy_static",
  "lru",
+ "num_cpus",
  "parity-scale-codec",
  "parking_lot 0.12.0",
  "paste 1.0.6",
@@ -8221,6 +8231,7 @@ dependencies = [
  "sp-version",
  "sp-wasm-interface",
  "substrate-test-runtime",
+ "tempfile",
  "tracing",
  "tracing-subscriber",
  "wasmi",
@@ -8274,6 +8285,7 @@ dependencies = [
  "sp-runtime-interface",
  "sp-sandbox",
  "sp-wasm-interface",
+ "tempfile",
  "wasmtime",
  "wat",
 ]
@@ -11838,6 +11850,7 @@ dependencies = [
  "libc",
  "log",
  "mach",
+ "memfd",
  "memoffset",
  "more-asserts",
  "rand 0.8.4",

substrate/bin/node/cli/benches/block_production.rs

@@ -29,7 +29,7 @@ use sc_consensus::{
 use sc_service::{
 	config::{
 		DatabaseSource, KeepBlocks, KeystoreConfig, NetworkConfiguration, OffchainWorkerConfig,
-		PruningMode, WasmExecutionMethod,
+		PruningMode, WasmExecutionMethod, WasmtimeInstantiationStrategy,
 	},
 	BasePath, Configuration, Role,
 };
@@ -77,7 +77,9 @@ fn new_node(tokio_handle: Handle) -> node_cli::service::NewFullBase {
 		state_pruning: Some(PruningMode::ArchiveAll),
 		keep_blocks: KeepBlocks::All,
 		chain_spec: spec,
-		wasm_method: WasmExecutionMethod::Compiled,
+		wasm_method: WasmExecutionMethod::Compiled {
+			instantiation_strategy: WasmtimeInstantiationStrategy::PoolingCopyOnWrite,
+		},
 		execution_strategies: ExecutionStrategies {
 			syncing: execution_strategy,
 			importing: execution_strategy,

substrate/bin/node/executor/benches/bench.rs

@@ -25,6 +25,8 @@ use node_runtime::{
 	UncheckedExtrinsic,
 };
 use node_testing::keyring::*;
+#[cfg(feature = "wasmtime")]
+use sc_executor::WasmtimeInstantiationStrategy;
 use sc_executor::{Externalities, NativeElseWasmExecutor, RuntimeVersionOf, WasmExecutionMethod};
 use sp_core::{
 	storage::well_known_keys,
@@ -183,7 +185,9 @@ fn bench_execute_block(c: &mut Criterion) {
 		ExecutionMethod::Native,
 		ExecutionMethod::Wasm(WasmExecutionMethod::Interpreted),
 		#[cfg(feature = "wasmtime")]
-		ExecutionMethod::Wasm(WasmExecutionMethod::Compiled),
+		ExecutionMethod::Wasm(WasmExecutionMethod::Compiled {
+			instantiation_strategy: WasmtimeInstantiationStrategy::PoolingCopyOnWrite,
+		}),
 	];
 
 	for strategy in execution_methods {

substrate/bin/node/testing/src/bench.rs

@@ -46,7 +46,7 @@ use sc_client_api::{
 };
 use sc_client_db::PruningMode;
 use sc_consensus::{BlockImport, BlockImportParams, ForkChoiceStrategy, ImportResult, ImportedAux};
-use sc_executor::{NativeElseWasmExecutor, WasmExecutionMethod};
+use sc_executor::{NativeElseWasmExecutor, WasmExecutionMethod, WasmtimeInstantiationStrategy};
 use sp_api::ProvideRuntimeApi;
 use sp_block_builder::BlockBuilder;
 use sp_consensus::BlockOrigin;
@@ -398,7 +398,14 @@ impl BenchDb {
 		let backend = sc_service::new_db_backend(db_config).expect("Should not fail");
 		let client = sc_service::new_client(
 			backend.clone(),
-			NativeElseWasmExecutor::new(WasmExecutionMethod::Compiled, None, 8, 2),
+			NativeElseWasmExecutor::new(
+				WasmExecutionMethod::Compiled {
+					instantiation_strategy: WasmtimeInstantiationStrategy::PoolingCopyOnWrite,
+				},
+				None,
+				8,
+				2,
+			),
 			&keyring.generate_genesis(),
 			None,
 			None,

substrate/client/cli/src/arg_enums.rs

@@ -20,6 +20,36 @@
 
 use clap::ArgEnum;
 
+/// The instantiation strategy to use in compiled mode.
+#[derive(Debug, Clone, Copy, ArgEnum)]
+#[clap(rename_all = "kebab-case")]
+pub enum WasmtimeInstantiationStrategy {
+	/// Pool the instances to avoid initializing everything from scratch
+	/// on each instantiation. Use copy-on-write memory when possible.
+	PoolingCopyOnWrite,
+
+	/// Recreate the instance from scratch on every instantiation.
+	/// Use copy-on-write memory when possible.
+	RecreateInstanceCopyOnWrite,
+
+	/// Pool the instances to avoid initializing everything from scratch
+	/// on each instantiation.
+	Pooling,
+
+	/// Recreate the instance from scratch on every instantiation. Very slow.
+	RecreateInstance,
+
+	/// Legacy instance reuse mechanism. DEPRECATED. Will be removed in the future.
+	///
+	/// Should only be used in case of encountering any issues with the new default
+	/// instantiation strategy.
+	LegacyInstanceReuse,
+}
+
+/// The default [`WasmtimeInstantiationStrategy`].
+pub const DEFAULT_WASMTIME_INSTANTIATION_STRATEGY: WasmtimeInstantiationStrategy =
+	WasmtimeInstantiationStrategy::PoolingCopyOnWrite;
+
 /// How to execute Wasm runtime code.
 #[derive(Debug, Clone, Copy)]
 pub enum WasmExecutionMethod {
@@ -71,18 +101,33 @@ impl WasmExecutionMethod {
 	}
 }
 
-impl Into<sc_service::config::WasmExecutionMethod> for WasmExecutionMethod {
-	fn into(self) -> sc_service::config::WasmExecutionMethod {
-		match self {
-			WasmExecutionMethod::Interpreted =>
-				sc_service::config::WasmExecutionMethod::Interpreted,
-			#[cfg(feature = "wasmtime")]
-			WasmExecutionMethod::Compiled => sc_service::config::WasmExecutionMethod::Compiled,
-			#[cfg(not(feature = "wasmtime"))]
-			WasmExecutionMethod::Compiled => panic!(
-				"Substrate must be compiled with \"wasmtime\" feature for compiled Wasm execution"
-			),
-		}
+/// Converts the execution method and instantiation strategy command line arguments
+/// into an execution method which can be used internally.
+pub fn execution_method_from_cli(
+	execution_method: WasmExecutionMethod,
+	_instantiation_strategy: WasmtimeInstantiationStrategy,
+) -> sc_service::config::WasmExecutionMethod {
+	match execution_method {
+		WasmExecutionMethod::Interpreted => sc_service::config::WasmExecutionMethod::Interpreted,
+		#[cfg(feature = "wasmtime")]
+		WasmExecutionMethod::Compiled => sc_service::config::WasmExecutionMethod::Compiled {
+			instantiation_strategy: match _instantiation_strategy {
+				WasmtimeInstantiationStrategy::PoolingCopyOnWrite =>
+					sc_service::config::WasmtimeInstantiationStrategy::PoolingCopyOnWrite,
+				WasmtimeInstantiationStrategy::RecreateInstanceCopyOnWrite =>
+					sc_service::config::WasmtimeInstantiationStrategy::RecreateInstanceCopyOnWrite,
+				WasmtimeInstantiationStrategy::Pooling =>
+					sc_service::config::WasmtimeInstantiationStrategy::Pooling,
+				WasmtimeInstantiationStrategy::RecreateInstance =>
+					sc_service::config::WasmtimeInstantiationStrategy::RecreateInstance,
+				WasmtimeInstantiationStrategy::LegacyInstanceReuse =>
+					sc_service::config::WasmtimeInstantiationStrategy::LegacyInstanceReuse,
+			},
+		},
+		#[cfg(not(feature = "wasmtime"))]
+		WasmExecutionMethod::Compiled => panic!(
+			"Substrate must be compiled with \"wasmtime\" feature for compiled Wasm execution"
+		),
 	}
 }
 

substrate/client/cli/src/params/import_params.rs

@@ -18,10 +18,11 @@
 
 use crate::{
 	arg_enums::{
-		ExecutionStrategy, WasmExecutionMethod, DEFAULT_EXECUTION_BLOCK_CONSTRUCTION,
-		DEFAULT_EXECUTION_IMPORT_BLOCK, DEFAULT_EXECUTION_IMPORT_BLOCK_VALIDATOR,
-		DEFAULT_EXECUTION_OFFCHAIN_WORKER, DEFAULT_EXECUTION_OTHER, DEFAULT_EXECUTION_SYNCING,
-		DEFAULT_WASM_EXECUTION_METHOD,
+		ExecutionStrategy, WasmExecutionMethod, WasmtimeInstantiationStrategy,
+		DEFAULT_EXECUTION_BLOCK_CONSTRUCTION, DEFAULT_EXECUTION_IMPORT_BLOCK,
+		DEFAULT_EXECUTION_IMPORT_BLOCK_VALIDATOR, DEFAULT_EXECUTION_OFFCHAIN_WORKER,
+		DEFAULT_EXECUTION_OTHER, DEFAULT_EXECUTION_SYNCING,
+		DEFAULT_WASMTIME_INSTANTIATION_STRATEGY, DEFAULT_WASM_EXECUTION_METHOD,
 	},
 	params::{DatabaseParams, PruningParams},
 };
@@ -62,6 +63,27 @@ pub struct ImportParams {
 	)]
 	pub wasm_method: WasmExecutionMethod,
 
+	/// The WASM instantiation method to use.
+	///
+	/// Only has an effect when `wasm-execution` is set to `compiled`.
+	///
+	/// The copy-on-write strategies are only supported on Linux.
+	/// If the copy-on-write variant of a strategy is unsupported
+	/// the executor will fall back to the non-CoW equivalent.
+	///
+	/// The fastest (and the default) strategy available is `pooling-copy-on-write`.
+	///
+	/// The `legacy-instance-reuse` strategy is deprecated and will
+	/// be removed in the future. It should only be used in case of
+	/// issues with the default instantiation strategy.
+	#[clap(
+		long,
+		value_name = "STRATEGY",
+		default_value_t = DEFAULT_WASMTIME_INSTANTIATION_STRATEGY,
+		arg_enum,
+	)]
+	pub wasmtime_instantiation_strategy: WasmtimeInstantiationStrategy,
+
 	/// Specify the path where local WASM runtimes are stored.
 	///
 	/// These runtimes will override on-chain runtimes when the version matches.
@@ -85,7 +107,7 @@ impl ImportParams {
 
 	/// Get the WASM execution method from the parameters
 	pub fn wasm_method(&self) -> sc_service::config::WasmExecutionMethod {
-		self.wasm_method.into()
+		crate::execution_method_from_cli(self.wasm_method, self.wasmtime_instantiation_strategy)
 	}
 
 	/// Enable overriding on-chain WASM with locally-stored WASM

substrate/client/executor/Cargo.toml

@@ -50,6 +50,8 @@ paste = "1.0"
 regex = "1.5.5"
 criterion = "0.3"
 env_logger = "0.9"
+num_cpus = "1.13.1"
+tempfile = "3.3.0"
 
 [[bench]]
 name = "bench"

substrate/client/executor/benches/bench.rs

@@ -17,26 +17,43 @@
 
 use criterion::{criterion_group, criterion_main, Criterion};
 
-use sc_executor_common::{runtime_blob::RuntimeBlob, wasm_runtime::WasmModule};
+use codec::Encode;
+
+use sc_executor_common::{
+	runtime_blob::RuntimeBlob,
+	wasm_runtime::{WasmInstance, WasmModule},
+};
+#[cfg(feature = "wasmtime")]
+use sc_executor_wasmtime::InstantiationStrategy;
 use sc_runtime_test::wasm_binary_unwrap as test_runtime;
 use sp_wasm_interface::HostFunctions as _;
-use std::sync::Arc;
+use std::sync::{
+	atomic::{AtomicBool, AtomicUsize, Ordering},
+	Arc,
+};
 
+#[derive(Clone)]
 enum Method {
 	Interpreted,
 	#[cfg(feature = "wasmtime")]
 	Compiled {
-		fast_instance_reuse: bool,
+		instantiation_strategy: InstantiationStrategy,
+		precompile: bool,
 	},
 }
 
-// This is just a bog-standard Kusama runtime with the extra `test_empty_return`
-// function copy-pasted from the test runtime.
+// This is just a bog-standard Kusama runtime with an extra
+// `test_empty_return` and `test_dirty_plenty_memory` functions
+// copy-pasted from the test runtime.
 fn kusama_runtime() -> &'static [u8] {
 	include_bytes!("kusama_runtime.wasm")
 }
 
-fn initialize(runtime: &[u8], method: Method) -> Arc<dyn WasmModule> {
+fn initialize(
+	_tmpdir: &mut Option<tempfile::TempDir>,
+	runtime: &[u8],
+	method: Method,
+) -> Arc<dyn WasmModule> {
 	let blob = RuntimeBlob::uncompress_if_needed(runtime).unwrap();
 	let host_functions = sp_io::SubstrateHostFunctions::host_functions();
 	let heap_pages = 2048;
@@ -51,80 +68,200 @@ fn initialize(runtime: &[u8], method: Method) -> Arc<dyn WasmModule> {
 		)
 		.map(|runtime| -> Arc<dyn WasmModule> { Arc::new(runtime) }),
 		#[cfg(feature = "wasmtime")]
-		Method::Compiled { fast_instance_reuse } =>
-			sc_executor_wasmtime::create_runtime::<sp_io::SubstrateHostFunctions>(
-				blob,
-				sc_executor_wasmtime::Config {
+		Method::Compiled { instantiation_strategy, precompile } => {
+			let config = sc_executor_wasmtime::Config {
+				allow_missing_func_imports,
+				cache_path: None,
+				semantics: sc_executor_wasmtime::Semantics {
+					extra_heap_pages: heap_pages,
+					instantiation_strategy,
+					deterministic_stack_limit: None,
+					canonicalize_nans: false,
+					parallel_compilation: true,
 					max_memory_size: None,
-					allow_missing_func_imports,
-					cache_path: None,
-					semantics: sc_executor_wasmtime::Semantics {
-						extra_heap_pages: heap_pages,
-						fast_instance_reuse,
-						deterministic_stack_limit: None,
-						canonicalize_nans: false,
-						parallel_compilation: true,
-					},
 				},
-			)
-			.map(|runtime| -> Arc<dyn WasmModule> { Arc::new(runtime) }),
+			};
+
+			if precompile {
+				let precompiled_blob =
+					sc_executor_wasmtime::prepare_runtime_artifact(blob, &config.semantics)
+						.unwrap();
+
+				// Create a fresh temporary directory to make absolutely sure
+				// we'll use the right module.
+				*_tmpdir = Some(tempfile::tempdir().unwrap());
+				let tmpdir = _tmpdir.as_ref().unwrap();
+
+				let path = tmpdir.path().join("module.bin");
+				std::fs::write(&path, &precompiled_blob).unwrap();
+				unsafe {
+					sc_executor_wasmtime::create_runtime_from_artifact::<
+						sp_io::SubstrateHostFunctions,
+					>(&path, config)
+				}
+			} else {
+				sc_executor_wasmtime::create_runtime::<sp_io::SubstrateHostFunctions>(blob, config)
+			}
+			.map(|runtime| -> Arc<dyn WasmModule> { Arc::new(runtime) })
+		},
 	}
 	.unwrap()
 }
 
+fn run_benchmark(
+	c: &mut Criterion,
+	benchmark_name: &str,
+	thread_count: usize,
+	runtime: &dyn WasmModule,
+	testcase: impl Fn(&mut Box<dyn WasmInstance>) + Copy + Send + 'static,
+) {
+	c.bench_function(benchmark_name, |b| {
+		// Here we deliberately start a bunch of extra threads which will just
+		// keep on independently instantiating the runtime over and over again.
+		//
+		// We don't really have to measure how much time those take since the
+		// work done is essentially the same on each thread, and what we're
+		// interested in here is only how those extra threads affect the execution
+		// on the current thread.
+		//
+		// In an ideal case assuming we have enough CPU cores those extra threads
+		// shouldn't affect the main thread's runtime at all, however in practice
+		// they're not completely independent. There might be per-process
+		// locks in the kernel which are briefly held during instantiation, etc.,
+		// and how much those affect the execution here is what we want to measure.
+		let is_benchmark_running = Arc::new(AtomicBool::new(true));
+		let threads_running = Arc::new(AtomicUsize::new(0));
+		let aux_threads: Vec<_> = (0..thread_count - 1)
+			.map(|_| {
+				let mut instance = runtime.new_instance().unwrap();
+				let is_benchmark_running = is_benchmark_running.clone();
+				let threads_running = threads_running.clone();
+				std::thread::spawn(move || {
+					threads_running.fetch_add(1, Ordering::SeqCst);
+					while is_benchmark_running.load(Ordering::Relaxed) {
+						testcase(&mut instance);
+					}
+				})
+			})
+			.collect();
+
+		while threads_running.load(Ordering::SeqCst) != (thread_count - 1) {
+			std::thread::yield_now();
+		}
+
+		let mut instance = runtime.new_instance().unwrap();
+		b.iter(|| testcase(&mut instance));
+
+		is_benchmark_running.store(false, Ordering::SeqCst);
+		for thread in aux_threads {
+			thread.join().unwrap();
+		}
+	});
+}
+
 fn bench_call_instance(c: &mut Criterion) {
 	let _ = env_logger::try_init();
 
-	#[cfg(feature = "wasmtime")]
-	{
-		let runtime = initialize(test_runtime(), Method::Compiled { fast_instance_reuse: true });
-		c.bench_function("call_instance_test_runtime_with_fast_instance_reuse", |b| {
-			let mut instance = runtime.new_instance().unwrap();
-			b.iter(|| instance.call_export("test_empty_return", &[0]).unwrap())
-		});
+	let strategies = [
+		#[cfg(feature = "wasmtime")]
+		(
+			"legacy_instance_reuse",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::LegacyInstanceReuse,
+				precompile: false,
+			},
+		),
+		#[cfg(feature = "wasmtime")]
+		(
+			"recreate_instance_vanilla",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::RecreateInstance,
+				precompile: false,
+			},
+		),
+		#[cfg(feature = "wasmtime")]
+		(
+			"recreate_instance_cow_fresh",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::RecreateInstanceCopyOnWrite,
+				precompile: false,
+			},
+		),
+		#[cfg(feature = "wasmtime")]
+		(
+			"recreate_instance_cow_precompiled",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::RecreateInstanceCopyOnWrite,
+				precompile: true,
+			},
+		),
+		#[cfg(feature = "wasmtime")]
+		(
+			"pooling_vanilla",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::Pooling,
+				precompile: false,
+			},
+		),
+		#[cfg(feature = "wasmtime")]
+		(
+			"pooling_cow_fresh",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::PoolingCopyOnWrite,
+				precompile: false,
+			},
+		),
+		#[cfg(feature = "wasmtime")]
+		(
+			"pooling_cow_precompiled",
+			Method::Compiled {
+				instantiation_strategy: InstantiationStrategy::PoolingCopyOnWrite,
+				precompile: true,
+			},
+		),
+		("interpreted", Method::Interpreted),
+	];
+
+	let runtimes = [("kusama_runtime", kusama_runtime()), ("test_runtime", test_runtime())];
+
+	let thread_counts = [1, 2, 4, 8, 16];
+
+	fn test_call_empty_function(instance: &mut Box<dyn WasmInstance>) {
+		instance.call_export("test_empty_return", &[0]).unwrap();
 	}
 
-	#[cfg(feature = "wasmtime")]
-	{
-		let runtime = initialize(test_runtime(), Method::Compiled { fast_instance_reuse: false });
-		c.bench_function("call_instance_test_runtime_without_fast_instance_reuse", |b| {
-			let mut instance = runtime.new_instance().unwrap();
-			b.iter(|| instance.call_export("test_empty_return", &[0]).unwrap());
-		});
+	fn test_dirty_1mb_of_memory(instance: &mut Box<dyn WasmInstance>) {
+		instance.call_export("test_dirty_plenty_memory", &(0, 16).encode()).unwrap();
 	}
 
-	#[cfg(feature = "wasmtime")]
-	{
-		let runtime = initialize(kusama_runtime(), Method::Compiled { fast_instance_reuse: true });
-		c.bench_function("call_instance_kusama_runtime_with_fast_instance_reuse", |b| {
-			let mut instance = runtime.new_instance().unwrap();
-			b.iter(|| instance.call_export("test_empty_return", &[0]).unwrap())
-		});
-	}
+	let testcases = [
+		("call_empty_function", test_call_empty_function as fn(&mut Box<dyn WasmInstance>)),
+		("dirty_1mb_of_memory", test_dirty_1mb_of_memory),
+	];
 
-	#[cfg(feature = "wasmtime")]
-	{
-		let runtime = initialize(kusama_runtime(), Method::Compiled { fast_instance_reuse: false });
-		c.bench_function("call_instance_kusama_runtime_without_fast_instance_reuse", |b| {
-			let mut instance = runtime.new_instance().unwrap();
-			b.iter(|| instance.call_export("test_empty_return", &[0]).unwrap());
-		});
-	}
+	let num_cpus = num_cpus::get_physical();
+	let mut tmpdir = None;
 
-	{
-		let runtime = initialize(test_runtime(), Method::Interpreted);
-		c.bench_function("call_instance_test_runtime_interpreted", |b| {
-			let mut instance = runtime.new_instance().unwrap();
-			b.iter(|| instance.call_export("test_empty_return", &[0]).unwrap())
-		});
-	}
+	for (strategy_name, strategy) in strategies {
+		for (runtime_name, runtime) in runtimes {
+			let runtime = initialize(&mut tmpdir, runtime, strategy.clone());
 
-	{
-		let runtime = initialize(kusama_runtime(), Method::Interpreted);
-		c.bench_function("call_instance_kusama_runtime_interpreted", |b| {
-			let mut instance = runtime.new_instance().unwrap();
-			b.iter(|| instance.call_export("test_empty_return", &[0]).unwrap())
-		});
+			for (testcase_name, testcase) in testcases {
+				for thread_count in thread_counts {
+					if thread_count > num_cpus {
+						// If there are not enough cores available the benchmark is pointless.
+						continue
+					}
+
+					let benchmark_name = format!(
+						"{}_from_{}_with_{}_on_{}_threads",
+						testcase_name, runtime_name, strategy_name, thread_count
+					);
+
+					run_benchmark(c, &benchmark_name, thread_count, &*runtime, testcase);
+				}
+			}
+		}
 	}
 }
 

substrate/client/executor/src/integration_tests/linux.rs

@@ -38,7 +38,13 @@ fn memory_consumption_compiled() {
 	// For that we make a series of runtime calls, probing the RSS for the VMA matching the linear
 	// memory. After the call we expect RSS to be equal to 0.
 
-	let runtime = mk_test_runtime(WasmExecutionMethod::Compiled, 1024);
+	let runtime = mk_test_runtime(
+		WasmExecutionMethod::Compiled {
+			instantiation_strategy:
+				sc_executor_wasmtime::InstantiationStrategy::LegacyInstanceReuse,
+		},
+		1024,
+	);
 
 	let mut instance = runtime.new_instance().unwrap();
 	let heap_base = instance

substrate/client/executor/src/integration_tests/mod.rs

@@ -54,8 +54,42 @@ macro_rules! test_wasm_execution {
 
 			#[test]
 			#[cfg(feature = "wasmtime")]
-			fn [<$method_name _compiled>]() {
-				$method_name(WasmExecutionMethod::Compiled);
+			fn [<$method_name _compiled_recreate_instance_cow>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::RecreateInstanceCopyOnWrite
+				});
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_recreate_instance_vanilla>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::RecreateInstance
+				});
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_pooling_cow>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::PoolingCopyOnWrite
+				});
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_pooling_vanilla>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::Pooling
+				});
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_legacy_instance_reuse>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::LegacyInstanceReuse
+				});
 			}
 		}
 	};
@@ -88,14 +122,82 @@ macro_rules! test_wasm_execution_sandbox {
 
 			#[test]
 			#[cfg(feature = "wasmtime")]
-			fn [<$method_name _compiled_host_executor>]() {
-				$method_name(WasmExecutionMethod::Compiled, "_host");
+			fn [<$method_name _compiled_pooling_cow_host_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::PoolingCopyOnWrite
+				}, "_host");
 			}
 
 			#[test]
 			#[cfg(feature = "wasmtime")]
-			fn [<$method_name _compiled_embedded_executor>]() {
-				$method_name(WasmExecutionMethod::Compiled, "_embedded");
+			fn [<$method_name _compiled_pooling_cow_embedded_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::PoolingCopyOnWrite
+				}, "_embedded");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_pooling_vanilla_host_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::Pooling
+				}, "_host");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_pooling_vanilla_embedded_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::Pooling
+				}, "_embedded");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_recreate_instance_cow_host_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::RecreateInstanceCopyOnWrite
+				}, "_host");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_recreate_instance_cow_embedded_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::RecreateInstanceCopyOnWrite
+				}, "_embedded");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_recreate_instance_vanilla_host_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::RecreateInstance
+				}, "_host");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_recreate_instance_vanilla_embedded_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::RecreateInstance
+				}, "_embedded");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_legacy_instance_reuse_host_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::LegacyInstanceReuse
+				}, "_host");
+			}
+
+			#[test]
+			#[cfg(feature = "wasmtime")]
+			fn [<$method_name _compiled_legacy_instance_reuse_embedded_executor>]() {
+				$method_name(WasmExecutionMethod::Compiled {
+					instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy::LegacyInstanceReuse
+				}, "_embedded");
 			}
 		}
 	};
@@ -153,7 +255,7 @@ fn call_not_existing_function(wasm_method: WasmExecutionMethod) {
 			let expected = match wasm_method {
 				WasmExecutionMethod::Interpreted => "Trap: Host(Other(\"Function `missing_external` is only a stub. Calling a stub is not allowed.\"))",
 				#[cfg(feature = "wasmtime")]
-				WasmExecutionMethod::Compiled => "call to a missing function env:missing_external"
+				WasmExecutionMethod::Compiled { .. } => "call to a missing function env:missing_external"
 			};
 			assert_eq!(error.message, expected);
 		},
@@ -173,7 +275,7 @@ fn call_yet_another_not_existing_function(wasm_method: WasmExecutionMethod) {
 			let expected = match wasm_method {
 				WasmExecutionMethod::Interpreted => "Trap: Host(Other(\"Function `yet_another_missing_external` is only a stub. Calling a stub is not allowed.\"))",
 				#[cfg(feature = "wasmtime")]
-				WasmExecutionMethod::Compiled => "call to a missing function env:yet_another_missing_external"
+				WasmExecutionMethod::Compiled { .. } => "call to a missing function env:yet_another_missing_external"
 			};
 			assert_eq!(error.message, expected);
 		},
@@ -473,7 +575,9 @@ fn should_trap_when_heap_exhausted(wasm_method: WasmExecutionMethod) {
 
 	match err {
 		#[cfg(feature = "wasmtime")]
-		Error::AbortedDueToTrap(error) if wasm_method == WasmExecutionMethod::Compiled => {
+		Error::AbortedDueToTrap(error)
+			if matches!(wasm_method, WasmExecutionMethod::Compiled { .. }) =>
+		{
 			assert_eq!(
 				error.message,
 				r#"host code panicked while being called by the runtime: Failed to allocate memory: "Allocator ran out of space""#
@@ -807,7 +911,7 @@ fn unreachable_intrinsic(wasm_method: WasmExecutionMethod) {
 			let expected = match wasm_method {
 				WasmExecutionMethod::Interpreted => "Trap: Unreachable",
 				#[cfg(feature = "wasmtime")]
-				WasmExecutionMethod::Compiled => "wasm trap: wasm `unreachable` instruction executed",
+				WasmExecutionMethod::Compiled { .. } => "wasm trap: wasm `unreachable` instruction executed",
 			};
 			assert_eq!(error.message, expected);
 		},

substrate/client/executor/src/lib.rs

@@ -51,6 +51,9 @@ pub use wasmi;
 
 pub use sc_executor_common::{error, sandbox};
 
+#[cfg(feature = "wasmtime")]
+pub use sc_executor_wasmtime::InstantiationStrategy as WasmtimeInstantiationStrategy;
+
 /// Extracts the runtime version of a given runtime code.
 pub trait RuntimeVersionOf {
 	/// Extract [`RuntimeVersion`](sp_version::RuntimeVersion) of the given `runtime_code`.

substrate/client/executor/src/wasm_runtime.rs

@@ -46,7 +46,10 @@ pub enum WasmExecutionMethod {
 	Interpreted,
 	/// Uses the Wasmtime compiled runtime.
 	#[cfg(feature = "wasmtime")]
-	Compiled,
+	Compiled {
+		/// The instantiation strategy to use.
+		instantiation_strategy: sc_executor_wasmtime::InstantiationStrategy,
+	},
 }
 
 impl Default for WasmExecutionMethod {
@@ -71,6 +74,9 @@ struct VersionedRuntime {
 	module: Arc<dyn WasmModule>,
 	/// Runtime version according to `Core_version` if any.
 	version: Option<RuntimeVersion>,
+
+	// TODO: Remove this once the legacy instance reuse instantiation strategy
+	//       for `wasmtime` is gone, as this only makes sense with that particular strategy.
 	/// Cached instance pool.
 	instances: Arc<Vec<Mutex<Option<Box<dyn WasmInstance>>>>>,
 }
@@ -310,22 +316,23 @@ where
 			.map(|runtime| -> Arc<dyn WasmModule> { Arc::new(runtime) })
 		},
 		#[cfg(feature = "wasmtime")]
-		WasmExecutionMethod::Compiled => sc_executor_wasmtime::create_runtime::<H>(
-			blob,
-			sc_executor_wasmtime::Config {
-				max_memory_size: None,
-				allow_missing_func_imports,
-				cache_path: cache_path.map(ToOwned::to_owned),
-				semantics: sc_executor_wasmtime::Semantics {
-					extra_heap_pages: heap_pages,
-					fast_instance_reuse: true,
-					deterministic_stack_limit: None,
-					canonicalize_nans: false,
-					parallel_compilation: true,
+		WasmExecutionMethod::Compiled { instantiation_strategy } =>
+			sc_executor_wasmtime::create_runtime::<H>(
+				blob,
+				sc_executor_wasmtime::Config {
+					allow_missing_func_imports,
+					cache_path: cache_path.map(ToOwned::to_owned),
+					semantics: sc_executor_wasmtime::Semantics {
+						extra_heap_pages: heap_pages,
+						instantiation_strategy,
+						deterministic_stack_limit: None,
+						canonicalize_nans: false,
+						parallel_compilation: true,
+						max_memory_size: None,
+					},
 				},
-			},
-		)
-		.map(|runtime| -> Arc<dyn WasmModule> { Arc::new(runtime) }),
+			)
+			.map(|runtime| -> Arc<dyn WasmModule> { Arc::new(runtime) }),
 	}
 }
 

substrate/client/executor/wasmtime/Cargo.toml

@@ -23,6 +23,8 @@ wasmtime = { version = "0.35.3", default-features = false, features = [
 	"cranelift",
 	"jitdump",
 	"parallel-compilation",
+	"memory-init-cow",
+	"pooling-allocator",
 ] }
 sc-allocator = { version = "4.1.0-dev", path = "../../allocator" }
 sc-executor-common = { version = "0.10.0-dev", path = "../common" }
@@ -34,3 +36,4 @@ sp-wasm-interface = { version = "6.0.0", features = ["wasmtime"], path = "../../
 wat = "1.0"
 sc-runtime-test = { version = "2.0.0", path = "../runtime-test" }
 sp-io = { version = "6.0.0", path = "../../../primitives/io" }
+tempfile = "3.3.0"

substrate/client/executor/wasmtime/src/lib.rs

@@ -38,5 +38,5 @@ mod tests;
 
 pub use runtime::{
 	create_runtime, create_runtime_from_artifact, prepare_runtime_artifact, Config,
-	DeterministicStackLimit, Semantics,
+	DeterministicStackLimit, InstantiationStrategy, Semantics,
 };

substrate/client/executor/wasmtime/src/runtime.rs

@@ -80,7 +80,7 @@ impl StoreData {
 pub(crate) type Store = wasmtime::Store<StoreData>;
 
 enum Strategy {
-	FastInstanceReuse {
+	LegacyInstanceReuse {
 		instance_wrapper: InstanceWrapper,
 		globals_snapshot: GlobalsSnapshot<wasmtime::Global>,
 		data_segments_snapshot: Arc<DataSegmentsSnapshot>,
@@ -136,41 +136,42 @@ struct InstanceSnapshotData {
 pub struct WasmtimeRuntime {
 	engine: wasmtime::Engine,
 	instance_pre: Arc<wasmtime::InstancePre<StoreData>>,
-	snapshot_data: Option<InstanceSnapshotData>,
+	instantiation_strategy: InternalInstantiationStrategy,
 	config: Config,
 }
 
 impl WasmModule for WasmtimeRuntime {
 	fn new_instance(&self) -> Result<Box<dyn WasmInstance>> {
-		let strategy = if let Some(ref snapshot_data) = self.snapshot_data {
-			let mut instance_wrapper = InstanceWrapper::new(
-				&self.engine,
-				&self.instance_pre,
-				self.config.max_memory_size,
-			)?;
-			let heap_base = instance_wrapper.extract_heap_base()?;
+		let strategy = match self.instantiation_strategy {
+			InternalInstantiationStrategy::LegacyInstanceReuse(ref snapshot_data) => {
+				let mut instance_wrapper = InstanceWrapper::new(
+					&self.engine,
+					&self.instance_pre,
+					self.config.semantics.max_memory_size,
+				)?;
+				let heap_base = instance_wrapper.extract_heap_base()?;
 
-			// This function panics if the instance was created from a runtime blob different from
-			// which the mutable globals were collected. Here, it is easy to see that there is only
-			// a single runtime blob and thus it's the same that was used for both creating the
-			// instance and collecting the mutable globals.
-			let globals_snapshot = GlobalsSnapshot::take(
-				&snapshot_data.mutable_globals,
-				&mut InstanceGlobals { instance: &mut instance_wrapper },
-			);
+				// This function panics if the instance was created from a runtime blob different
+				// from which the mutable globals were collected. Here, it is easy to see that there
+				// is only a single runtime blob and thus it's the same that was used for both
+				// creating the instance and collecting the mutable globals.
+				let globals_snapshot = GlobalsSnapshot::take(
+					&snapshot_data.mutable_globals,
+					&mut InstanceGlobals { instance: &mut instance_wrapper },
+				);
 
-			Strategy::FastInstanceReuse {
-				instance_wrapper,
-				globals_snapshot,
-				data_segments_snapshot: snapshot_data.data_segments_snapshot.clone(),
-				heap_base,
-			}
-		} else {
-			Strategy::RecreateInstance(InstanceCreator {
+				Strategy::LegacyInstanceReuse {
+					instance_wrapper,
+					globals_snapshot,
+					data_segments_snapshot: snapshot_data.data_segments_snapshot.clone(),
+					heap_base,
+				}
+			},
+			InternalInstantiationStrategy::Builtin => Strategy::RecreateInstance(InstanceCreator {
 				engine: self.engine.clone(),
 				instance_pre: self.instance_pre.clone(),
-				max_memory_size: self.config.max_memory_size,
-			})
+				max_memory_size: self.config.semantics.max_memory_size,
+			}),
 		};
 
 		Ok(Box::new(WasmtimeInstance { strategy }))
@@ -186,7 +187,7 @@ pub struct WasmtimeInstance {
 impl WasmInstance for WasmtimeInstance {
 	fn call(&mut self, method: InvokeMethod, data: &[u8]) -> Result<Vec<u8>> {
 		match &mut self.strategy {
-			Strategy::FastInstanceReuse {
+			Strategy::LegacyInstanceReuse {
 				ref mut instance_wrapper,
 				globals_snapshot,
 				data_segments_snapshot,
@@ -225,7 +226,7 @@ impl WasmInstance for WasmtimeInstance {
 
 	fn get_global_const(&mut self, name: &str) -> Result<Option<Value>> {
 		match &mut self.strategy {
-			Strategy::FastInstanceReuse { instance_wrapper, .. } =>
+			Strategy::LegacyInstanceReuse { instance_wrapper, .. } =>
 				instance_wrapper.get_global_val(name),
 			Strategy::RecreateInstance(ref mut instance_creator) =>
 				instance_creator.instantiate()?.get_global_val(name),
@@ -239,7 +240,7 @@ impl WasmInstance for WasmtimeInstance {
 				// associated with it.
 				None
 			},
-			Strategy::FastInstanceReuse { instance_wrapper, .. } =>
+			Strategy::LegacyInstanceReuse { instance_wrapper, .. } =>
 				Some(instance_wrapper.base_ptr()),
 		}
 	}
@@ -326,6 +327,48 @@ fn common_config(semantics: &Semantics) -> std::result::Result<wasmtime::Config,
 	config.wasm_threads(false);
 	config.wasm_memory64(false);
 
+	let (use_pooling, use_cow) = match semantics.instantiation_strategy {
+		InstantiationStrategy::PoolingCopyOnWrite => (true, true),
+		InstantiationStrategy::Pooling => (true, false),
+		InstantiationStrategy::RecreateInstanceCopyOnWrite => (false, true),
+		InstantiationStrategy::RecreateInstance => (false, false),
+		InstantiationStrategy::LegacyInstanceReuse => (false, false),
+	};
+
+	config.memory_init_cow(use_cow);
+	config.memory_guaranteed_dense_image_size(
+		semantics.max_memory_size.map(|max| max as u64).unwrap_or(u64::MAX),
+	);
+
+	if use_pooling {
+		config.allocation_strategy(wasmtime::InstanceAllocationStrategy::Pooling {
+			strategy: wasmtime::PoolingAllocationStrategy::ReuseAffinity,
+
+			// Pooling needs a bunch of hard limits to be set; if we go over
+			// any of these then the instantiation will fail.
+			instance_limits: wasmtime::InstanceLimits {
+				// Current minimum values for kusama (as of 2022-04-14):
+				//   size: 32384
+				//   table_elements: 1249
+				//   memory_pages: 2070
+				size: 64 * 1024,
+				table_elements: 2048,
+				memory_pages: 4096,
+
+				// We can only have a single of those.
+				tables: 1,
+				memories: 1,
+
+				// This determines how many instances of the module can be
+				// instantiated in parallel from the same `Module`.
+				//
+				// This includes nested instances spawned with `sp_tasks::spawn`
+				// from *within* the runtime.
+				count: 32,
+			},
+		});
+	}
+
 	Ok(config)
 }
 
@@ -373,18 +416,47 @@ pub struct DeterministicStackLimit {
 	pub native_stack_max: u32,
 }
 
+/// The instantiation strategy to use for the WASM executor.
+///
+/// All of the CoW strategies (with `CopyOnWrite` suffix) are only supported when either:
+///   a) we're running on Linux,
+///   b) we're running on an Unix-like system and we're precompiling
+///      our module beforehand.
+///
+/// If the CoW variant of a strategy is unsupported the executor will
+/// fall back to the non-CoW equivalent.
+#[non_exhaustive]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+pub enum InstantiationStrategy {
+	/// Pool the instances to avoid initializing everything from scratch
+	/// on each instantiation. Use copy-on-write memory when possible.
+	///
+	/// This is the fastest instantiation strategy.
+	PoolingCopyOnWrite,
+
+	/// Recreate the instance from scratch on every instantiation.
+	/// Use copy-on-write memory when possible.
+	RecreateInstanceCopyOnWrite,
+
+	/// Pool the instances to avoid initializing everything from scratch
+	/// on each instantiation.
+	Pooling,
+
+	/// Recreate the instance from scratch on every instantiation. Very slow.
+	RecreateInstance,
+
+	/// Legacy instance reuse mechanism. DEPRECATED. Will be removed. Do not use.
+	LegacyInstanceReuse,
+}
+
+enum InternalInstantiationStrategy {
+	LegacyInstanceReuse(InstanceSnapshotData),
+	Builtin,
+}
+
 pub struct Semantics {
-	/// Enabling this will lead to some optimization shenanigans that make calling [`WasmInstance`]
-	/// extremely fast.
-	///
-	/// Primarily this is achieved by not recreating the instance for each call and performing a
-	/// bare minimum clean up: reapplying the data segments and restoring the values for global
-	/// variables.
-	///
-	/// Since this feature depends on instrumentation, it can be set only if runtime is
-	/// instantiated using the runtime blob, e.g. using [`create_runtime`].
-	// I.e. if [`CodeSupplyMode::Verbatim`] is used.
-	pub fast_instance_reuse: bool,
+	/// The instantiation strategy to use.
+	pub instantiation_strategy: InstantiationStrategy,
 
 	/// Specifying `Some` will enable deterministic stack height. That is, all executor
 	/// invocations will reach stack overflow at the exactly same point across different wasmtime
@@ -418,9 +490,7 @@ pub struct Semantics {
 	/// The number of extra WASM pages which will be allocated
 	/// on top of what is requested by the WASM blob itself.
 	pub extra_heap_pages: u64,
-}
 
-pub struct Config {
 	/// The total amount of memory in bytes an instance can request.
 	///
 	/// If specified, the runtime will be able to allocate only that much of wasm memory.
@@ -436,7 +506,9 @@ pub struct Config {
 	///
 	/// The default is `None`.
 	pub max_memory_size: Option<usize>,
+}
 
+pub struct Config {
 	/// The WebAssembly standard requires all imports of an instantiated module to be resolved,
 	/// otherwise, the instantiation fails. If this option is set to `true`, then this behavior is
 	/// overriden and imports that are requested by the module and not provided by the host
@@ -452,24 +524,16 @@ pub struct Config {
 
 enum CodeSupplyMode<'a> {
 	/// The runtime is instantiated using the given runtime blob.
-	Verbatim {
-		// Rationale to take the `RuntimeBlob` here is so that the client will be able to reuse
-		// the blob e.g. if they did a prevalidation. If they didn't they can pass a `RuntimeBlob`
-		// instance and it will be used anyway in most cases, because we are going to do at least
-		// some instrumentations for both anticipated paths: substrate execution and PVF execution.
-		//
-		// Should there raise a need in performing no instrumentation and the client doesn't need
-		// to do any checks, then we can provide a `Cow` like semantics here: if we need the blob
-		// and  the user got `RuntimeBlob` then extract it, or otherwise create it from the given
-		// bytecode.
-		blob: RuntimeBlob,
-	},
+	Fresh(RuntimeBlob),
 
-	/// The code is supplied in a form of a compiled artifact.
+	/// The runtime is instantiated using a precompiled module.
 	///
 	/// This assumes that the code is already prepared for execution and the same `Config` was
 	/// used.
-	Artifact { compiled_artifact: &'a [u8] },
+	///
+	/// We use a `Path` here instead of simply passing a byte slice to allow `wasmtime` to
+	/// map the runtime's linear memory on supported platforms in a copy-on-write fashion.
+	Precompiled(&'a Path),
 }
 
 /// Create a new `WasmtimeRuntime` given the code. This function performs translation from Wasm to
@@ -484,29 +548,34 @@ pub fn create_runtime<H>(
 where
 	H: HostFunctions,
 {
-	// SAFETY: this is safe because it doesn't use `CodeSupplyMode::Artifact`.
-	unsafe { do_create_runtime::<H>(CodeSupplyMode::Verbatim { blob }, config) }
+	// SAFETY: this is safe because it doesn't use `CodeSupplyMode::Precompiled`.
+	unsafe { do_create_runtime::<H>(CodeSupplyMode::Fresh(blob), config) }
 }
 
-/// The same as [`create_runtime`] but takes a precompiled artifact, which makes this function
-/// considerably faster than [`create_runtime`].
+/// The same as [`create_runtime`] but takes a path to a precompiled artifact,
+/// which makes this function considerably faster than [`create_runtime`].
 ///
 /// # Safety
 ///
-/// The caller must ensure that the compiled artifact passed here was produced by
-/// [`prepare_runtime_artifact`]. Otherwise, there is a risk of arbitrary code execution with all
-/// implications.
+/// The caller must ensure that the compiled artifact passed here was:
+///   1) produced by [`prepare_runtime_artifact`],
+///   2) written to the disk as a file,
+///   3) was not modified,
+///   4) will not be modified while any runtime using this artifact is alive, or is being
+///      instantiated.
 ///
-/// It is ok though if the `compiled_artifact` was created by code of another version or with
+/// Failure to adhere to these requirements might lead to crashes and arbitrary code execution.
+///
+/// It is ok though if the compiled artifact was created by code of another version or with
 /// different configuration flags. In such case the caller will receive an `Err` deterministically.
 pub unsafe fn create_runtime_from_artifact<H>(
-	compiled_artifact: &[u8],
+	compiled_artifact_path: &Path,
 	config: Config,
 ) -> std::result::Result<WasmtimeRuntime, WasmError>
 where
 	H: HostFunctions,
 {
-	do_create_runtime::<H>(CodeSupplyMode::Artifact { compiled_artifact }, config)
+	do_create_runtime::<H>(CodeSupplyMode::Precompiled(compiled_artifact_path), config)
 }
 
 /// # Safety
@@ -520,7 +589,6 @@ unsafe fn do_create_runtime<H>(
 where
 	H: HostFunctions,
 {
-	// Create the engine, store and finally the module from the given code.
 	let mut wasmtime_config = common_config(&config.semantics)?;
 	if let Some(ref cache_path) = config.cache_path {
 		if let Err(reason) = setup_wasmtime_caching(cache_path, &mut wasmtime_config) {
@@ -534,45 +602,71 @@ where
 	let engine = Engine::new(&wasmtime_config)
 		.map_err(|e| WasmError::Other(format!("cannot create the wasmtime engine: {}", e)))?;
 
-	let (module, snapshot_data) = match code_supply_mode {
-		CodeSupplyMode::Verbatim { blob } => {
+	let (module, instantiation_strategy) = match code_supply_mode {
+		CodeSupplyMode::Fresh(blob) => {
 			let blob = prepare_blob_for_compilation(blob, &config.semantics)?;
 			let serialized_blob = blob.clone().serialize();
 
 			let module = wasmtime::Module::new(&engine, &serialized_blob)
 				.map_err(|e| WasmError::Other(format!("cannot create module: {}", e)))?;
 
-			if config.semantics.fast_instance_reuse {
-				let data_segments_snapshot = DataSegmentsSnapshot::take(&blob).map_err(|e| {
-					WasmError::Other(format!("cannot take data segments snapshot: {}", e))
-				})?;
-				let data_segments_snapshot = Arc::new(data_segments_snapshot);
-				let mutable_globals = ExposedMutableGlobalsSet::collect(&blob);
+			match config.semantics.instantiation_strategy {
+				InstantiationStrategy::LegacyInstanceReuse => {
+					let data_segments_snapshot =
+						DataSegmentsSnapshot::take(&blob).map_err(|e| {
+							WasmError::Other(format!("cannot take data segments snapshot: {}", e))
+						})?;
+					let data_segments_snapshot = Arc::new(data_segments_snapshot);
+					let mutable_globals = ExposedMutableGlobalsSet::collect(&blob);
 
-				(module, Some(InstanceSnapshotData { data_segments_snapshot, mutable_globals }))
-			} else {
-				(module, None)
+					(
+						module,
+						InternalInstantiationStrategy::LegacyInstanceReuse(InstanceSnapshotData {
+							data_segments_snapshot,
+							mutable_globals,
+						}),
+					)
+				},
+				InstantiationStrategy::Pooling |
+				InstantiationStrategy::PoolingCopyOnWrite |
+				InstantiationStrategy::RecreateInstance |
+				InstantiationStrategy::RecreateInstanceCopyOnWrite =>
+					(module, InternalInstantiationStrategy::Builtin),
 			}
 		},
-		CodeSupplyMode::Artifact { compiled_artifact } => {
-			// SAFETY: The unsafity of `deserialize` is covered by this function. The
+		CodeSupplyMode::Precompiled(compiled_artifact_path) => {
+			if let InstantiationStrategy::LegacyInstanceReuse =
+				config.semantics.instantiation_strategy
+			{
+				return Err(WasmError::Other("the legacy instance reuse instantiation strategy is incompatible with precompiled modules".into()));
+			}
+
+			// SAFETY: The unsafety of `deserialize_file` is covered by this function. The
 			//         responsibilities to maintain the invariants are passed to the caller.
-			let module = wasmtime::Module::deserialize(&engine, compiled_artifact)
+			//
+			//         See [`create_runtime_from_artifact`] for more details.
+			let module = wasmtime::Module::deserialize_file(&engine, compiled_artifact_path)
 				.map_err(|e| WasmError::Other(format!("cannot deserialize module: {}", e)))?;
 
-			(module, None)
+			(module, InternalInstantiationStrategy::Builtin)
 		},
 	};
 
 	let mut linker = wasmtime::Linker::new(&engine);
 	crate::imports::prepare_imports::<H>(&mut linker, &module, config.allow_missing_func_imports)?;
 
-	let mut store = crate::instance_wrapper::create_store(module.engine(), config.max_memory_size);
+	let mut store =
+		crate::instance_wrapper::create_store(module.engine(), config.semantics.max_memory_size);
 	let instance_pre = linker
 		.instantiate_pre(&mut store, &module)
 		.map_err(|e| WasmError::Other(format!("cannot preinstantiate module: {}", e)))?;
 
-	Ok(WasmtimeRuntime { engine, instance_pre: Arc::new(instance_pre), snapshot_data, config })
+	Ok(WasmtimeRuntime {
+		engine,
+		instance_pre: Arc::new(instance_pre),
+		instantiation_strategy,
+		config,
+	})
 }
 
 fn prepare_blob_for_compilation(
@@ -583,16 +677,17 @@ fn prepare_blob_for_compilation(
 		blob = blob.inject_stack_depth_metering(logical_max)?;
 	}
 
-	// If enabled, this should happen after all other passes that may introduce global variables.
-	if semantics.fast_instance_reuse {
+	if let InstantiationStrategy::LegacyInstanceReuse = semantics.instantiation_strategy {
+		// When this strategy is used this must be called after all other passes which may introduce
+		// new global variables, otherwise they will not be reset when we call into the runtime
+		// again.
 		blob.expose_mutable_globals();
 	}
 
 	// We don't actually need the memory to be imported so we can just convert any memory
 	// import into an export with impunity. This simplifies our code since `wasmtime` will
-	// now automatically take care of creating the memory for us, and it also allows us
-	// to potentially enable `wasmtime`'s instance pooling at a later date. (Imported
-	// memories are ineligible for pooling.)
+	// now automatically take care of creating the memory for us, and it is also necessary
+	// to enable `wasmtime`'s instance pooling. (Imported memories are ineligible for pooling.)
 	blob.convert_memory_import_into_export()?;
 	blob.add_extra_heap_pages_to_memory_section(
 		semantics

substrate/client/executor/wasmtime/src/tests.rs

@@ -19,18 +19,20 @@
 use codec::{Decode as _, Encode as _};
 use sc_executor_common::{error::Error, runtime_blob::RuntimeBlob, wasm_runtime::WasmModule};
 use sc_runtime_test::wasm_binary_unwrap;
-use std::sync::Arc;
+
+use crate::InstantiationStrategy;
 
 type HostFunctions = sp_io::SubstrateHostFunctions;
 
 struct RuntimeBuilder {
 	code: Option<String>,
-	fast_instance_reuse: bool,
+	instantiation_strategy: InstantiationStrategy,
 	canonicalize_nans: bool,
 	deterministic_stack: bool,
 	extra_heap_pages: u64,
 	max_memory_size: Option<usize>,
 	precompile_runtime: bool,
+	tmpdir: Option<tempfile::TempDir>,
 }
 
 impl RuntimeBuilder {
@@ -39,41 +41,42 @@ impl RuntimeBuilder {
 	fn new_on_demand() -> Self {
 		Self {
 			code: None,
-			fast_instance_reuse: false,
+			instantiation_strategy: InstantiationStrategy::RecreateInstance,
 			canonicalize_nans: false,
 			deterministic_stack: false,
 			extra_heap_pages: 1024,
 			max_memory_size: None,
 			precompile_runtime: false,
+			tmpdir: None,
 		}
 	}
 
-	fn use_wat(&mut self, code: String) -> &mut Self {
+	fn use_wat(mut self, code: String) -> Self {
 		self.code = Some(code);
 		self
 	}
 
-	fn canonicalize_nans(&mut self, canonicalize_nans: bool) -> &mut Self {
+	fn canonicalize_nans(mut self, canonicalize_nans: bool) -> Self {
 		self.canonicalize_nans = canonicalize_nans;
 		self
 	}
 
-	fn deterministic_stack(&mut self, deterministic_stack: bool) -> &mut Self {
+	fn deterministic_stack(mut self, deterministic_stack: bool) -> Self {
 		self.deterministic_stack = deterministic_stack;
 		self
 	}
 
-	fn precompile_runtime(&mut self, precompile_runtime: bool) -> &mut Self {
+	fn precompile_runtime(mut self, precompile_runtime: bool) -> Self {
 		self.precompile_runtime = precompile_runtime;
 		self
 	}
 
-	fn max_memory_size(&mut self, max_memory_size: Option<usize>) -> &mut Self {
+	fn max_memory_size(mut self, max_memory_size: Option<usize>) -> Self {
 		self.max_memory_size = max_memory_size;
 		self
 	}
 
-	fn build(&mut self) -> Arc<dyn WasmModule> {
+	fn build<'a>(&'a mut self) -> impl WasmModule + 'a {
 		let blob = {
 			let wasm: Vec<u8>;
 
@@ -90,11 +93,10 @@ impl RuntimeBuilder {
 		};
 
 		let config = crate::Config {
-			max_memory_size: self.max_memory_size,
 			allow_missing_func_imports: true,
 			cache_path: None,
 			semantics: crate::Semantics {
-				fast_instance_reuse: self.fast_instance_reuse,
+				instantiation_strategy: self.instantiation_strategy,
 				deterministic_stack_limit: match self.deterministic_stack {
 					true => Some(crate::DeterministicStackLimit {
 						logical_max: 65536,
@@ -105,24 +107,31 @@ impl RuntimeBuilder {
 				canonicalize_nans: self.canonicalize_nans,
 				parallel_compilation: true,
 				extra_heap_pages: self.extra_heap_pages,
+				max_memory_size: self.max_memory_size,
 			},
 		};
 
-		let rt = if self.precompile_runtime {
+		if self.precompile_runtime {
+			let dir = tempfile::tempdir().unwrap();
+			let path = dir.path().join("runtime.bin");
+
+			// Delay the removal of the temporary directory until we're dropped.
+			self.tmpdir = Some(dir);
+
 			let artifact = crate::prepare_runtime_artifact(blob, &config.semantics).unwrap();
-			unsafe { crate::create_runtime_from_artifact::<HostFunctions>(&artifact, config) }
+			std::fs::write(&path, artifact).unwrap();
+			unsafe { crate::create_runtime_from_artifact::<HostFunctions>(&path, config) }
 		} else {
 			crate::create_runtime::<HostFunctions>(blob, config)
 		}
-		.expect("cannot create runtime");
-
-		Arc::new(rt) as Arc<dyn WasmModule>
+		.expect("cannot create runtime")
 	}
 }
 
 #[test]
 fn test_nan_canonicalization() {
-	let runtime = RuntimeBuilder::new_on_demand().canonicalize_nans(true).build();
+	let mut builder = RuntimeBuilder::new_on_demand().canonicalize_nans(true);
+	let runtime = builder.build();
 
 	let mut instance = runtime.new_instance().expect("failed to instantiate a runtime");
 
@@ -161,10 +170,11 @@ fn test_nan_canonicalization() {
 fn test_stack_depth_reaching() {
 	const TEST_GUARD_PAGE_SKIP: &str = include_str!("test-guard-page-skip.wat");
 
-	let runtime = RuntimeBuilder::new_on_demand()
+	let mut builder = RuntimeBuilder::new_on_demand()
 		.use_wat(TEST_GUARD_PAGE_SKIP.to_string())
-		.deterministic_stack(true)
-		.build();
+		.deterministic_stack(true);
+
+	let runtime = builder.build();
 	let mut instance = runtime.new_instance().expect("failed to instantiate a runtime");
 
 	match instance.call_export("test-many-locals", &[]).unwrap_err() {
@@ -202,11 +212,12 @@ fn test_max_memory_pages(import_memory: bool, precompile_runtime: bool) {
 		wat: String,
 		precompile_runtime: bool,
 	) -> Result<(), Box<dyn std::error::Error>> {
-		let runtime = RuntimeBuilder::new_on_demand()
+		let mut builder = RuntimeBuilder::new_on_demand()
 			.use_wat(wat)
 			.max_memory_size(max_memory_size)
-			.precompile_runtime(precompile_runtime)
-			.build();
+			.precompile_runtime(precompile_runtime);
+
+		let runtime = builder.build();
 		let mut instance = runtime.new_instance()?;
 		let _ = instance.call_export("main", &[])?;
 		Ok(())
@@ -377,15 +388,15 @@ fn test_instances_without_reuse_are_not_leaked() {
 	let runtime = crate::create_runtime::<HostFunctions>(
 		RuntimeBlob::uncompress_if_needed(wasm_binary_unwrap()).unwrap(),
 		crate::Config {
-			max_memory_size: None,
 			allow_missing_func_imports: true,
 			cache_path: None,
 			semantics: crate::Semantics {
-				fast_instance_reuse: false,
+				instantiation_strategy: InstantiationStrategy::RecreateInstance,
 				deterministic_stack_limit: None,
 				canonicalize_nans: false,
 				parallel_compilation: true,
 				extra_heap_pages: 2048,
+				max_memory_size: None,
 			},
 		},
 	)

substrate/client/service/src/config.rs

@@ -21,6 +21,8 @@
 pub use sc_client_api::execution_extensions::{ExecutionStrategies, ExecutionStrategy};
 pub use sc_client_db::{Database, DatabaseSource, KeepBlocks, PruningMode};
 pub use sc_executor::WasmExecutionMethod;
+#[cfg(feature = "wasmtime")]
+pub use sc_executor::WasmtimeInstantiationStrategy;
 pub use sc_network::{
 	config::{
 		MultiaddrWithPeerId, NetworkConfiguration, NodeKeyConfig, NonDefaultSetConfig, Role,

substrate/utils/frame/benchmarking-cli/src/pallet/command.rs

@@ -23,7 +23,9 @@ use frame_benchmarking::{
 };
 use frame_support::traits::StorageInfo;
 use linked_hash_map::LinkedHashMap;
-use sc_cli::{CliConfiguration, ExecutionStrategy, Result, SharedParams};
+use sc_cli::{
+	execution_method_from_cli, CliConfiguration, ExecutionStrategy, Result, SharedParams,
+};
 use sc_client_db::BenchmarkingState;
 use sc_executor::NativeElseWasmExecutor;
 use sc_service::{Configuration, NativeExecutionDispatch};
@@ -121,7 +123,6 @@ impl PalletCmd {
 		}
 
 		let spec = config.chain_spec;
-		let wasm_method = self.wasm_method.into();
 		let strategy = self.execution.unwrap_or(ExecutionStrategy::Native);
 		let pallet = self.pallet.clone().unwrap_or_default();
 		let pallet = pallet.as_bytes();
@@ -141,7 +142,7 @@ impl PalletCmd {
 		let state_without_tracking =
 			BenchmarkingState::<BB>::new(genesis_storage, cache_size, self.record_proof, false)?;
 		let executor = NativeElseWasmExecutor::<ExecDispatch>::new(
-			wasm_method,
+			execution_method_from_cli(self.wasm_method, self.wasmtime_instantiation_strategy),
 			self.heap_pages,
 			2, // The runtime instances cache size.
 			2, // The runtime cache size

substrate/utils/frame/benchmarking-cli/src/pallet/mod.rs

@@ -18,7 +18,10 @@
 mod command;
 mod writer;
 
-use sc_cli::{ExecutionStrategy, WasmExecutionMethod, DEFAULT_WASM_EXECUTION_METHOD};
+use sc_cli::{
+	ExecutionStrategy, WasmExecutionMethod, WasmtimeInstantiationStrategy,
+	DEFAULT_WASMTIME_INSTANTIATION_STRATEGY, DEFAULT_WASM_EXECUTION_METHOD,
+};
 use std::{fmt::Debug, path::PathBuf};
 
 // Add a more relaxed parsing for pallet names by allowing pallet directory names with `-` to be
@@ -131,6 +134,17 @@ pub struct PalletCmd {
 	)]
 	pub wasm_method: WasmExecutionMethod,
 
+	/// The WASM instantiation method to use.
+	///
+	/// Only has an effect when `wasm-execution` is set to `compiled`.
+	#[clap(
+		long = "wasm-instantiation-strategy",
+		value_name = "STRATEGY",
+		default_value_t = DEFAULT_WASMTIME_INSTANTIATION_STRATEGY,
+		arg_enum,
+	)]
+	pub wasmtime_instantiation_strategy: WasmtimeInstantiationStrategy,
+
 	/// Limit the memory the database cache can use.
 	#[clap(long = "db-cache", value_name = "MiB", default_value = "1024")]
 	pub database_cache_size: u32,

substrate/utils/frame/try-runtime/cli/src/lib.rs

@@ -271,7 +271,9 @@ use remote_externalities::{
 };
 use sc_chain_spec::ChainSpec;
 use sc_cli::{
-	CliConfiguration, ExecutionStrategy, WasmExecutionMethod, DEFAULT_WASM_EXECUTION_METHOD,
+	execution_method_from_cli, CliConfiguration, ExecutionStrategy, WasmExecutionMethod,
+	WasmtimeInstantiationStrategy, DEFAULT_WASMTIME_INSTANTIATION_STRATEGY,
+	DEFAULT_WASM_EXECUTION_METHOD,
 };
 use sc_executor::NativeElseWasmExecutor;
 use sc_service::{Configuration, NativeExecutionDispatch};
@@ -400,6 +402,17 @@ pub struct SharedParams {
 	)]
 	pub wasm_method: WasmExecutionMethod,
 
+	/// The WASM instantiation method to use.
+	///
+	/// Only has an effect when `wasm-execution` is set to `compiled`.
+	#[clap(
+		long = "wasm-instantiation-strategy",
+		value_name = "STRATEGY",
+		default_value_t = DEFAULT_WASMTIME_INSTANTIATION_STRATEGY,
+		arg_enum,
+	)]
+	pub wasmtime_instantiation_strategy: WasmtimeInstantiationStrategy,
+
 	/// The number of 64KB pages to allocate for Wasm execution. Defaults to
 	/// [`sc_service::Configuration.default_heap_pages`].
 	#[clap(long)]
@@ -675,13 +688,12 @@ pub(crate) fn build_executor<D: NativeExecutionDispatch + 'static>(
 	shared: &SharedParams,
 	config: &sc_service::Configuration,
 ) -> NativeElseWasmExecutor<D> {
-	let wasm_method = shared.wasm_method;
 	let heap_pages = shared.heap_pages.or(config.default_heap_pages);
 	let max_runtime_instances = config.max_runtime_instances;
 	let runtime_cache_size = config.runtime_cache_size;
 
 	NativeElseWasmExecutor::<D>::new(
-		wasm_method.into(),
+		execution_method_from_cli(shared.wasm_method, shared.wasmtime_instantiation_strategy),
 		heap_pages,
 		max_runtime_instances,
 		runtime_cache_size,