From 0290afe1f8eafabf71695d677807e07658d078ab Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Mon, 15 Mar 2021 18:27:26 +0100
Subject: [PATCH] Make block rc code more understandable

---
 src/garage/admin_rpc.rs | 18 ++++++++++++++
 src/model/block.rs      | 54 ++++++++++++++++-------------------------
 src/table/merkle.rs     |  2 +-
 3 files changed, 40 insertions(+), 34 deletions(-)

diff --git a/src/garage/admin_rpc.rs b/src/garage/admin_rpc.rs
index a75c9013..512e00dd 100644
--- a/src/garage/admin_rpc.rs
+++ b/src/garage/admin_rpc.rs
@@ -423,6 +423,12 @@ impl AdminRpcHandler {
 		self.gather_table_stats(&mut ret, &self.garage.block_ref_table, &opt)?;
 
 		writeln!(&mut ret, "\nBlock manager stats:").unwrap();
+		writeln!(
+			&mut ret,
+			"  number of blocks: {}",
+			self.garage.block_manager.rc.len()
+		)
+		.unwrap();
 		writeln!(
 			&mut ret,
 			"  resync queue length: {}",
@@ -451,6 +457,18 @@ impl AdminRpcHandler {
 			t.data.merkle_updater.todo.len()
 		)
 		.unwrap();
+		writeln!(
+			to,
+			"  Merkle tree size: {}",
+			t.data.merkle_updater.merkle_tree.len()
+		)
+		.unwrap();
+		writeln!(
+			to,
+			"  GC todo queue length: {}",
+			t.data.gc_todo.len()
+		)
+		.unwrap();
 		Ok(())
 	}
 }
diff --git a/src/model/block.rs b/src/model/block.rs
index 36ad867a..8523474a 100644
--- a/src/model/block.rs
+++ b/src/model/block.rs
@@ -77,7 +77,6 @@ impl BlockManager {
 		let rc = db
 			.open_tree("block_local_rc")
 			.expect("Unable to open block_local_rc tree");
-		rc.set_merge_operator(rc_merge);
 
 		let resync_queue = db
 			.open_tree("block_local_resync_queue")
@@ -194,7 +193,7 @@ impl BlockManager {
 		let needed = self
 			.rc
 			.get(hash.as_ref())?
-			.map(|x| u64_from_bytes(x.as_ref()) > 0)
+			.map(|x| u64_from_be_bytes(x) > 0)
 			.unwrap_or(false);
 		if needed {
 			let path = self.block_path(hash);
@@ -218,17 +217,27 @@ impl BlockManager {
 	}
 
 	pub fn block_incref(&self, hash: &Hash) -> Result<(), Error> {
-		let old_rc = self.rc.get(&hash)?;
-		self.rc.merge(&hash, vec![1])?;
-		if old_rc.map(|x| u64_from_bytes(&x[..]) == 0).unwrap_or(true) {
+		let old_rc = self.rc.fetch_and_update(&hash, |old| {
+			let old_v = old.map(u64_from_be_bytes).unwrap_or(0);
+			Some(u64::to_be_bytes(old_v + 1).to_vec())
+		})?;
+		let old_rc = old_rc.map(u64_from_be_bytes).unwrap_or(0);
+		if old_rc == 0 {
 			self.put_to_resync(&hash, BLOCK_RW_TIMEOUT)?;
 		}
 		Ok(())
 	}
 
 	pub fn block_decref(&self, hash: &Hash) -> Result<(), Error> {
-		let new_rc = self.rc.merge(&hash, vec![0])?;
-		if new_rc.map(|x| u64_from_bytes(&x[..]) == 0).unwrap_or(true) {
+		let new_rc = self.rc.update_and_fetch(&hash, |old| {
+			let old_v = old.map(u64_from_be_bytes).unwrap_or(0);
+			if old_v > 1 {
+				Some(u64::to_be_bytes(old_v - 1).to_vec())
+			} else {
+				None
+			}
+		})?;
+		if new_rc.is_none() {
 			self.put_to_resync(&hash, BLOCK_GC_TIMEOUT)?;
 		}
 		Ok(())
@@ -251,7 +260,7 @@ impl BlockManager {
 		let mut n_failures = 0usize;
 		while !*must_exit.borrow() {
 			if let Some((time_bytes, hash_bytes)) = self.resync_queue.pop_min()? {
-				let time_msec = u64_from_bytes(&time_bytes[0..8]);
+				let time_msec = u64_from_be_bytes(&time_bytes[0..8]);
 				let now = now_msec();
 				if now >= time_msec {
 					let hash = Hash::try_from(&hash_bytes[..]).unwrap();
@@ -295,7 +304,7 @@ impl BlockManager {
 		let needed = self
 			.rc
 			.get(hash.as_ref())?
-			.map(|x| u64_from_bytes(x.as_ref()) > 0)
+			.map(|x| u64_from_be_bytes(x) > 0)
 			.unwrap_or(false);
 
 		if exists != needed {
@@ -487,30 +496,9 @@ impl BlockManager {
 	}
 }
 
-fn u64_from_bytes(bytes: &[u8]) -> u64 {
-	assert!(bytes.len() == 8);
+fn u64_from_be_bytes<T: AsRef<[u8]>>(bytes: T) -> u64 {
+	assert!(bytes.as_ref().len() == 8);
 	let mut x8 = [0u8; 8];
-	x8.copy_from_slice(bytes);
+	x8.copy_from_slice(bytes.as_ref());
 	u64::from_be_bytes(x8)
 }
-
-fn rc_merge(_key: &[u8], old: Option<&[u8]>, new: &[u8]) -> Option<Vec<u8>> {
-	let old = old.map(u64_from_bytes).unwrap_or(0);
-	assert!(new.len() == 1);
-	let new = match new[0] {
-		0 => {
-			if old > 0 {
-				old - 1
-			} else {
-				0
-			}
-		}
-		1 => old + 1,
-		_ => unreachable!(),
-	};
-	if new == 0 {
-		None
-	} else {
-		Some(u64::to_be_bytes(new).to_vec())
-	}
-}
diff --git a/src/table/merkle.rs b/src/table/merkle.rs
index 7a0adba1..a917a028 100644
--- a/src/table/merkle.rs
+++ b/src/table/merkle.rs
@@ -46,7 +46,7 @@ pub struct MerkleUpdater {
 	// Content of the merkle tree: items where
 	// - key = .bytes() for MerkleNodeKey
 	// - value = serialization of a MerkleNode, assumed to be MerkleNode::empty if not found
-	pub(crate) merkle_tree: sled::Tree,
+	pub merkle_tree: sled::Tree,
 	empty_node_hash: Hash,
 }