[fix-buffering] implement block_ram_buffer_max to avoid excessive RAM usage

src/block/manager.rs

@@ -1,3 +1,4 @@
+use std::convert::TryInto;
 use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::Duration;
@@ -10,7 +11,7 @@ use serde::{Deserialize, Serialize};
 
 use tokio::fs;
 use tokio::io::{AsyncReadExt, AsyncWriteExt, BufReader};
-use tokio::sync::{mpsc, Mutex, MutexGuard};
+use tokio::sync::{mpsc, Mutex, MutexGuard, Semaphore};
 
 use opentelemetry::{
 	trace::{FutureExt as OtelFutureExt, TraceContextExt, Tracer},
@@ -93,6 +94,7 @@ pub struct BlockManager {
 
 	pub(crate) system: Arc<System>,
 	pub(crate) endpoint: Arc<Endpoint<BlockRpc, Self>>,
+	buffer_kb_semaphore: Arc<Semaphore>,
 
 	pub(crate) metrics: BlockManagerMetrics,
 
@@ -152,11 +154,14 @@ impl BlockManager {
 			.netapp
 			.endpoint("garage_block/manager.rs/Rpc".to_string());
 
+		let buffer_kb_semaphore = Arc::new(Semaphore::new(config.block_ram_buffer_max / 1024));
+
 		let metrics = BlockManagerMetrics::new(
 			config.compression_level,
 			rc.rc.clone(),
 			resync.queue.clone(),
 			resync.errors.clone(),
+			buffer_kb_semaphore.clone(),
 		);
 
 		let scrub_persister = PersisterShared::new(&system.metadata_dir, "scrub_info");
@@ -176,6 +181,7 @@ impl BlockManager {
 			resync,
 			system,
 			endpoint,
+			buffer_kb_semaphore,
 			metrics,
 			scrub_persister,
 			tx_scrub_command: ArcSwapOption::new(None),
@@ -361,6 +367,14 @@ impl BlockManager {
 		let (header, bytes) = DataBlock::from_buffer(data, self.compression_level)
 			.await
 			.into_parts();
+
+		let permit = self
+			.buffer_kb_semaphore
+			.clone()
+			.acquire_many_owned((bytes.len() / 1024).try_into().unwrap())
+			.await
+			.ok_or_message("could not reserve space for buffer of data to send to remote nodes")?;
+
 		let put_block_rpc =
 			Req::new(BlockRpc::PutBlock { hash, header })?.with_stream_from_buffer(bytes);
 		let put_block_rpc = if let Some(tag) = order_tag {
@@ -376,6 +390,7 @@ impl BlockManager {
 				&who[..],
 				put_block_rpc,
 				RequestStrategy::with_priority(PRIO_NORMAL | PRIO_SECONDARY)
+					.with_drop_on_completion(permit)
 					.with_quorum(self.replication.write_quorum()),
 			)
 			.await?;

src/block/metrics.rs

@@ -1,3 +1,7 @@
+use std::sync::Arc;
+
+use tokio::sync::Semaphore;
+
 use opentelemetry::{global, metrics::*};
 
 use garage_db as db;
@@ -9,6 +13,7 @@ pub struct BlockManagerMetrics {
 	pub(crate) _rc_size: ValueObserver<u64>,
 	pub(crate) _resync_queue_len: ValueObserver<u64>,
 	pub(crate) _resync_errored_blocks: ValueObserver<u64>,
+	pub(crate) _buffer_free_kb: ValueObserver<u64>,
 
 	pub(crate) resync_counter: BoundCounter<u64>,
 	pub(crate) resync_error_counter: BoundCounter<u64>,
@@ -31,6 +36,7 @@ impl BlockManagerMetrics {
 		rc_tree: db::Tree,
 		resync_queue: CountedTree,
 		resync_errors: CountedTree,
+		buffer_semaphore: Arc<Semaphore>,
 	) -> Self {
 		let meter = global::meter("garage_model/block");
 		Self {
@@ -66,6 +72,15 @@ impl BlockManagerMetrics {
 				.with_description("Number of block hashes whose last resync resulted in an error")
 				.init(),
 
+			_buffer_free_kb: meter
+				.u64_value_observer("block.ram_buffer_free_kb", move |observer| {
+					observer.observe(buffer_semaphore.available_permits() as u64, &[])
+				})
+				.with_description(
+					"Available RAM in KiB to use for buffering data blocks to be written to remote nodes",
+				)
+				.init(),
+
 			resync_counter: meter
 				.u64_counter("block.resync_counter")
 				.with_description("Number of calls to resync_block")

src/model/k2v/rpc.rs

@@ -300,7 +300,11 @@ impl K2VRpcHandler {
 		let rs = RequestStrategy::with_priority(PRIO_NORMAL).without_timeout();
 		let mut requests = nodes
 			.iter()
-			.map(|node| self.system.rpc.call(&self.endpoint, *node, msg.clone(), rs))
+			.map(|node| {
+				self.system
+					.rpc
+					.call(&self.endpoint, *node, msg.clone(), rs.clone())
+			})
 			.collect::<FuturesUnordered<_>>();
 
 		// Fetch responses. This procedure stops fetching responses when any of the following

src/rpc/rpc_helper.rs

@@ -33,8 +33,7 @@ use crate::ring::Ring;
 const DEFAULT_TIMEOUT: Duration = Duration::from_secs(300);
 
 /// Strategy to apply when making RPC
-#[derive(Copy, Clone)]
-pub struct RequestStrategy {
+pub struct RequestStrategy<T> {
 	/// Min number of response to consider the request successful
 	pub rs_quorum: Option<usize>,
 	/// Should requests be dropped after enough response are received
@@ -43,6 +42,8 @@ pub struct RequestStrategy {
 	pub rs_priority: RequestPriority,
 	/// Custom timeout for this request
 	rs_timeout: Timeout,
+	/// Data to drop when everything completes
+	rs_drop_on_complete: T,
 }
 
 #[derive(Copy, Clone)]
@@ -52,7 +53,19 @@ enum Timeout {
 	Custom(Duration),
 }
 
-impl RequestStrategy {
+impl Clone for RequestStrategy<()> {
+	fn clone(&self) -> Self {
+		RequestStrategy {
+			rs_quorum: self.rs_quorum,
+			rs_interrupt_after_quorum: self.rs_interrupt_after_quorum,
+			rs_priority: self.rs_priority,
+			rs_timeout: self.rs_timeout,
+			rs_drop_on_complete: (),
+		}
+	}
+}
+
+impl RequestStrategy<()> {
 	/// Create a RequestStrategy with default timeout and not interrupting when quorum reached
 	pub fn with_priority(prio: RequestPriority) -> Self {
 		RequestStrategy {
@@ -60,8 +73,22 @@ impl RequestStrategy {
 			rs_interrupt_after_quorum: false,
 			rs_priority: prio,
 			rs_timeout: Timeout::Default,
+			rs_drop_on_complete: (),
 		}
 	}
+	/// Add an item to be dropped on completion
+	pub fn with_drop_on_completion<T>(self, drop_on_complete: T) -> RequestStrategy<T> {
+		RequestStrategy {
+			rs_quorum: self.rs_quorum,
+			rs_interrupt_after_quorum: self.rs_interrupt_after_quorum,
+			rs_priority: self.rs_priority,
+			rs_timeout: self.rs_timeout,
+			rs_drop_on_complete: drop_on_complete,
+		}
+	}
+}
+
+impl<T> RequestStrategy<T> {
 	/// Set quorum to be reached for request
 	pub fn with_quorum(mut self, quorum: usize) -> Self {
 		self.rs_quorum = Some(quorum);
@@ -83,6 +110,19 @@ impl RequestStrategy {
 		self.rs_timeout = Timeout::Custom(timeout);
 		self
 	}
+	/// Extract drop_on_complete item
+	fn extract_drop_on_complete(self) -> (RequestStrategy<()>, T) {
+		(
+			RequestStrategy {
+				rs_quorum: self.rs_quorum,
+				rs_interrupt_after_quorum: self.rs_interrupt_after_quorum,
+				rs_priority: self.rs_priority,
+				rs_timeout: self.rs_timeout,
+				rs_drop_on_complete: (),
+			},
+			self.rs_drop_on_complete,
+		)
+	}
 }
 
 #[derive(Clone)]
@@ -123,7 +163,7 @@ impl RpcHelper {
 		endpoint: &Endpoint<M, H>,
 		to: Uuid,
 		msg: N,
-		strat: RequestStrategy,
+		strat: RequestStrategy<()>,
 	) -> Result<S, Error>
 	where
 		M: Rpc<Response = Result<S, Error>>,
@@ -176,7 +216,7 @@ impl RpcHelper {
 		endpoint: &Endpoint<M, H>,
 		to: &[Uuid],
 		msg: N,
-		strat: RequestStrategy,
+		strat: RequestStrategy<()>,
 	) -> Result<Vec<(Uuid, Result<S, Error>)>, Error>
 	where
 		M: Rpc<Response = Result<S, Error>>,
@@ -187,7 +227,7 @@ impl RpcHelper {
 
 		let resps = join_all(
 			to.iter()
-				.map(|to| self.call(endpoint, *to, msg.clone(), strat)),
+				.map(|to| self.call(endpoint, *to, msg.clone(), strat.clone())),
 		)
 		.await;
 		Ok(to
@@ -201,7 +241,7 @@ impl RpcHelper {
 		&self,
 		endpoint: &Endpoint<M, H>,
 		msg: N,
-		strat: RequestStrategy,
+		strat: RequestStrategy<()>,
 	) -> Result<Vec<(Uuid, Result<S, Error>)>, Error>
 	where
 		M: Rpc<Response = Result<S, Error>>,
@@ -220,18 +260,19 @@ impl RpcHelper {
 
 	/// Make a RPC call to multiple servers, returning either a Vec of responses,
 	/// or an error if quorum could not be reached due to too many errors
-	pub async fn try_call_many<M, N, H, S>(
+	pub async fn try_call_many<M, N, H, S, T>(
 		&self,
 		endpoint: &Arc<Endpoint<M, H>>,
 		to: &[Uuid],
 		msg: N,
-		strategy: RequestStrategy,
+		strategy: RequestStrategy<T>,
 	) -> Result<Vec<S>, Error>
 	where
 		M: Rpc<Response = Result<S, Error>> + 'static,
 		N: IntoReq<M>,
 		H: StreamingEndpointHandler<M> + 'static,
 		S: Send + 'static,
+		T: Send + 'static,
 	{
 		let quorum = strategy.rs_quorum.unwrap_or(to.len());
 
@@ -260,12 +301,12 @@ impl RpcHelper {
 			.await
 	}
 
-	async fn try_call_many_internal<M, N, H, S>(
+	async fn try_call_many_internal<M, N, H, S, T>(
 		&self,
 		endpoint: &Arc<Endpoint<M, H>>,
 		to: &[Uuid],
 		msg: N,
-		strategy: RequestStrategy,
+		strategy: RequestStrategy<T>,
 		quorum: usize,
 	) -> Result<Vec<S>, Error>
 	where
@@ -273,9 +314,12 @@ impl RpcHelper {
 		N: IntoReq<M>,
 		H: StreamingEndpointHandler<M> + 'static,
 		S: Send + 'static,
+		T: Send + 'static,
 	{
 		let msg = msg.into_req().map_err(garage_net::error::Error::from)?;
 
+		let (strategy, drop_on_complete) = strategy.extract_drop_on_complete();
+
 		// Build future for each request
 		// They are not started now: they are added below in a FuturesUnordered
 		// object that will take care of polling them (see below)
@@ -283,6 +327,7 @@ impl RpcHelper {
 			let self2 = self.clone();
 			let msg = msg.clone();
 			let endpoint2 = endpoint.clone();
+			let strategy = strategy.clone();
 			(to, async move {
 				self2.call(&endpoint2, to, msg, strategy).await
 			})
@@ -377,6 +422,7 @@ impl RpcHelper {
 				// they have to be put in a proper queue that is persisted to disk.
 				tokio::spawn(async move {
 					resp_stream.collect::<Vec<Result<_, _>>>().await;
+					drop(drop_on_complete);
 				});
 			}
 		}

src/util/config.rs

@@ -52,6 +52,14 @@ pub struct Config {
 	)]
 	pub compression_level: Option<i32>,
 
+	/// Maximum amount of block data to buffer in RAM for sending to
+	/// remote nodes when these nodes are on slower links
+	#[serde(
+		deserialize_with = "deserialize_capacity",
+		default = "default_block_ram_buffer_max"
+	)]
+	pub block_ram_buffer_max: usize,
+
 	/// Skip the permission check of secret files. Useful when
 	/// POSIX ACLs (or more complex chmods) are used.
 	#[serde(default)]
@@ -255,6 +263,9 @@ fn default_sled_flush_every_ms() -> u64 {
 fn default_block_size() -> usize {
 	1048576
 }
+fn default_block_ram_buffer_max() -> usize {
+	256 * 1024 * 1024
+}
 
 fn default_compression() -> Option<i32> {
 	Some(1)