refactor: make cache eviction more aggressive when emergency

Signed-off-by: MrCroxx <[email protected]>

src/compute/src/memory/controller.rs

@@ -153,16 +153,17 @@ impl LruWatermarkController {
         let last_step = self.state.lru_watermark_step;
         let last_used_memory_bytes = self.state.used_memory_bytes;
 
-        let target_memory_bytes = self.threshold_graceful;
-        if cur_used_memory_bytes > target_memory_bytes {
-            let ratio =
-                (cur_used_memory_bytes - target_memory_bytes) as f64 / cur_used_memory_bytes as f64;
-            let latest_sequence = self.latest_sequence.load(Ordering::Relaxed);
-            let sequence_diff =
-                ((latest_sequence - self.evict_sequence) as f64 * ratio) as Sequence;
-            self.evict_sequence = latest_sequence.min(self.evict_sequence + sequence_diff);
-        }
-        let sequence = self.evict_sequence;
+        // * aggressive ~ inf        : x2
+        // *   graceful ~ aggressive : x1.5
+        // *     stable ~ graceful   : x1
+        // *          0 ~ stable     : no evict
+        let to_evict_bytes = cur_used_memory_bytes.saturating_sub(self.threshold_aggressive) / 2
+            + cur_used_memory_bytes.saturating_sub(self.threshold_graceful) / 2
+            + cur_used_memory_bytes.saturating_sub(self.threshold_stable);
+        let ratio = to_evict_bytes as f64 / cur_used_memory_bytes as f64;
+        let latest_sequence = self.latest_sequence.load(Ordering::Relaxed);
+        let sequence_diff = ((latest_sequence - self.evict_sequence) as f64 * ratio) as Sequence;
+        self.evict_sequence = latest_sequence.min(self.evict_sequence + sequence_diff);
 
         // The watermark calculation works in the following way:
         //
@@ -242,6 +243,9 @@ impl LruWatermarkController {
             .set(jvm_allocated_bytes as i64);
         self.metrics.jvm_active_bytes.set(jvm_active_bytes as i64);
 
-        (Epoch::from_physical_time(watermark_time_ms), sequence)
+        (
+            Epoch::from_physical_time(watermark_time_ms),
+            self.evict_sequence,
+        )
     }
 }