fix: kvcache evict workflow

src/instance/kv_cache.rs

@@ -10,6 +10,12 @@
 
 use ahash::AHashMap;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum L1Change {
+    Added(u64),
+    Removed(u64),
+}
+
 /// Doubly-linked-list-backed LRU keyed by block hash.
 #[derive(Debug)]
 pub struct LruBlocks {
@@ -56,6 +62,16 @@ impl LruBlocks {
         self.map.contains_key(&key)
     }
 
+    pub fn remove(&mut self, key: u64) -> bool {
+        if let Some(idx) = self.map.remove(&key) {
+            self.detach(idx);
+            self.free.push(idx);
+            true
+        } else {
+            false
+        }
+    }
+
     /// Touch (move to MRU) if present. Returns whether the key was present.
     pub fn touch(&mut self, key: u64) -> bool {
         if let Some(&idx) = self.map.get(&key) {
@@ -70,33 +86,47 @@ impl LruBlocks {
     /// existing block just touches it.
     pub fn insert_blocks(&mut self, hashes: &[u64], evicted_out: &mut Vec<u64>) {
         for &h in hashes {
-            if self.touch(h) {
-                continue;
+            if let Some(evicted) = self.insert_block(h) {
+                evicted_out.push(evicted);
             }
-            // need to make room?
-            if self.map.len() == self.capacity {
-                if let Some(tail_idx) = self.tail {
-                    let tail_key = self.nodes[tail_idx].key;
-                    self.detach(tail_idx);
-                    self.map.remove(&tail_key);
-                    self.free.push(tail_idx);
-                    evicted_out.push(tail_key);
-                }
-            }
-            // allocate node
-            let idx = if let Some(i) = self.free.pop() {
-                self.nodes[i] = Node { key: h, prev: None, next: None };
-                i
-            } else {
-                let i = self.nodes.len();
-                self.nodes.push(Node { key: h, prev: None, next: None });
-                i
-            };
-            self.map.insert(h, idx);
-            self.attach_to_head(idx);
         }
     }
 
+    pub fn insert_block(&mut self, key: u64) -> Option<u64> {
+        if self.touch(key) {
+            return None;
+        }
+        let mut evicted = None;
+        if self.map.len() == self.capacity {
+            if let Some(tail_idx) = self.tail {
+                let tail_key = self.nodes[tail_idx].key;
+                self.detach(tail_idx);
+                self.map.remove(&tail_key);
+                self.free.push(tail_idx);
+                evicted = Some(tail_key);
+            }
+        }
+        let idx = if let Some(i) = self.free.pop() {
+            self.nodes[i] = Node {
+                key,
+                prev: None,
+                next: None,
+            };
+            i
+        } else {
+            let i = self.nodes.len();
+            self.nodes.push(Node {
+                key,
+                prev: None,
+                next: None,
+            });
+            i
+        };
+        self.map.insert(key, idx);
+        self.attach_to_head(idx);
+        evicted
+    }
+
     /// Longest leading prefix of `hashes` present; touches the matched blocks.
     pub fn longest_prefix(&mut self, hashes: &[u64]) -> usize {
         let mut n = 0usize;
@@ -178,6 +208,68 @@ impl TwoTierCache {
             l1: LruBlocks::new(l1_cap),
         }
     }
+
+    pub fn insert_blocks_into_l0(&mut self, hashes: &[u64]) -> Vec<L1Change> {
+        let mut changes = Vec::new();
+        for &h in hashes {
+            self.insert_block_into_l0(h, &mut changes);
+        }
+        changes
+    }
+
+    pub fn promote_l1_blocks_to_l0(&mut self, hashes: &[u64]) -> Vec<L1Change> {
+        let mut changes = Vec::new();
+        for &h in hashes {
+            if self.l1.remove(h) {
+                changes.push(L1Change::Removed(h));
+            }
+            self.insert_block_into_l0(h, &mut changes);
+        }
+        changes
+    }
+
+    pub fn fetch_remote_blocks_to_l0(&mut self, hashes: &[u64]) -> Vec<L1Change> {
+        let mut changes = Vec::new();
+        for &h in hashes {
+            self.stage_remote_block_in_l1(h, &mut changes);
+            let removed = self.l1.remove(h);
+            debug_assert!(removed, "staged remote block must be present in l1");
+            self.insert_block_into_l0(h, &mut changes);
+        }
+        changes
+    }
+
+    fn insert_block_into_l0(&mut self, hash: u64, changes: &mut Vec<L1Change>) {
+        if self.l0.touch(hash) {
+            return;
+        }
+        if self.l1.remove(hash) {
+            changes.push(L1Change::Removed(hash));
+        }
+        if let Some(evicted_l0) = self.l0.insert_block(hash) {
+            self.demote_into_l1(evicted_l0, changes);
+        }
+    }
+
+    fn stage_remote_block_in_l1(&mut self, hash: u64, changes: &mut Vec<L1Change>) {
+        if self.l0.contains(hash) || self.l1.contains(hash) {
+            return;
+        }
+        if let Some(evicted_l1) = self.l1.insert_block(hash) {
+            changes.push(L1Change::Removed(evicted_l1));
+        }
+    }
+
+    fn demote_into_l1(&mut self, hash: u64, changes: &mut Vec<L1Change>) {
+        debug_assert!(!self.l0.contains(hash));
+        if self.l1.touch(hash) {
+            return;
+        }
+        if let Some(evicted_l1) = self.l1.insert_block(hash) {
+            changes.push(L1Change::Removed(evicted_l1));
+        }
+        changes.push(L1Change::Added(hash));
+    }
 }
 
 #[cfg(test)]
@@ -223,4 +315,61 @@ mod tests {
         c.insert_blocks(&[4], &mut ev);
         assert_eq!(ev, vec![2]);
     }
+
+    #[test]
+    fn two_tier_cache_demotes_l0_evictions_into_l1() {
+        let mut c = TwoTierCache::new(2, 2);
+
+        assert!(c.insert_blocks_into_l0(&[1, 2]).is_empty());
+        let changes = c.insert_blocks_into_l0(&[3]);
+
+        assert!(c.l0.contains(2));
+        assert!(c.l0.contains(3));
+        assert!(!c.l0.contains(1));
+        assert!(c.l1.contains(1));
+        assert_eq!(changes, vec![L1Change::Added(1)]);
+    }
+
+    #[test]
+    fn promoting_l1_blocks_to_l0_keeps_tiers_exclusive() {
+        let mut c = TwoTierCache::new(2, 2);
+        c.insert_blocks_into_l0(&[1, 2, 3]);
+
+        let changes = c.promote_l1_blocks_to_l0(&[1]);
+
+        assert!(c.l0.contains(1));
+        assert!(c.l0.contains(3));
+        assert!(!c.l0.contains(2));
+        assert!(!c.l1.contains(1));
+        assert!(c.l1.contains(2));
+        assert_eq!(changes, vec![L1Change::Removed(1), L1Change::Added(2)]);
+    }
+
+    #[test]
+    fn reinserting_block_into_l0_removes_duplicate_from_l1() {
+        let mut c = TwoTierCache::new(2, 2);
+        c.insert_blocks_into_l0(&[1, 2, 3]);
+
+        let changes = c.insert_blocks_into_l0(&[1]);
+
+        assert!(c.l0.contains(1));
+        assert!(c.l0.contains(3));
+        assert!(!c.l1.contains(1));
+        assert!(c.l1.contains(2));
+        assert_eq!(changes, vec![L1Change::Removed(1), L1Change::Added(2)]);
+    }
+
+    #[test]
+    fn remote_fetch_uses_l1_capacity_before_promoting_to_l0() {
+        let mut c = TwoTierCache::new(2, 1);
+        c.insert_blocks_into_l0(&[1, 2, 3]);
+
+        let changes = c.fetch_remote_blocks_to_l0(&[4]);
+
+        assert!(c.l0.contains(3));
+        assert!(c.l0.contains(4));
+        assert!(!c.l1.contains(1));
+        assert!(c.l1.contains(2));
+        assert_eq!(changes, vec![L1Change::Removed(1), L1Change::Added(2)]);
+    }
 }