Simple LRU garbage collection for interned values (#839)

* simple LRU garbage collection for interned values

* shard interned values

* gate memo size assertion to 64-bit platforms

* extend internal documentation for interned structs

* remove `first_interned_at` field from interned values

* clarify difference between tracked and interned structs

* only keep track of low durability interned values for garbage collection

Author: ibraheemdev

Cargo.toml

@@ -14,12 +14,11 @@ salsa-macros = { version = "0.22.0", path = "components/salsa-macros", optional
 
 boxcar = { version = "0.2.12" }
 crossbeam-queue = "0.3.11"
-dashmap = { version = "6", features = ["raw-api"] }
-# the version of hashbrown used by dashmap
-hashbrown_14 = { version = "0.14", package = "hashbrown" }
+crossbeam-utils = "0.8.21"
 hashbrown = "0.15"
 hashlink = "0.10"
 indexmap = "2"
+intrusive-collections = "0.9.7"
 parking_lot = "0.12"
 portable-atomic = "1"
 rustc-hash = "2"
@@ -52,6 +51,7 @@ salsa-macros = { version = "=0.22.0", path = "components/salsa-macros" }
 [dev-dependencies]
 # examples
 crossbeam-channel = "0.5.14"
+dashmap = { version = "6", features = ["raw-api"] }
 eyre = "0.6.8"
 notify-debouncer-mini = "0.4.1"
 ordered-float = "4.2.1"

src/durability.rs

@@ -87,14 +87,6 @@ impl Durability {
     pub(crate) fn index(self) -> usize {
         self.0 as usize
     }
-
-    pub(crate) fn as_u8(self) -> u8 {
-        self.0 as u8
-    }
-
-    pub(crate) fn from_u8(value: u8) -> Self {
-        Self(DurabilityVal::from(value))
-    }
 }
 
 impl Default for Durability {

src/event.rs

@@ -108,8 +108,17 @@ pub enum EventKind {
         revision: Revision,
     },
 
+    /// Indicates that a value was interned by reusing an existing slot.
+    DidReuseInternedValue {
+        // The key of the interned value.
+        key: DatabaseKeyIndex,
+
+        // The revision the value was interned in.
+        revision: Revision,
+    },
+
     /// Indicates that a previously interned value was read in a new revision.
-    DidReinternValue {
+    DidValidateInternedValue {
         // The key of the interned value.
         key: DatabaseKeyIndex,