Kv Cache Eviction

KV cache eviction is the policy for removing or compressing cached attention states when memory pressure grows, while preserving important context for ongoing generation - eviction strategy directly affects long-context quality and system stability.

What Is KV cache eviction?

• Definition: Controlled deletion of KV entries based on recency, importance, or budget limits.
• Trigger Conditions: Activated when cache occupancy approaches memory thresholds.
• Policy Types: Includes recency-based, attention-score-based, and hybrid importance eviction.
• Serving Context: Critical for long sessions, streaming workloads, and high-concurrency environments.

Why KV cache eviction Matters

• Memory Safety: Prevents out-of-memory failures during extended decoding workloads.
• Latency Stability: Managed eviction avoids emergency compaction and runtime stalls.
• Quality Preservation: Smart policies keep high-value tokens while dropping low-impact history.
• Capacity Scaling: Efficient eviction enables more simultaneous requests per device.
• Operational Control: Policy tuning provides explicit tradeoff knobs for quality versus cost.

How It Is Used in Practice

• Importance Scoring: Estimate token utility from attention statistics and structural markers.
• Tiered Memory: Move low-priority states to slower storage before full eviction when possible.
• Guardrail Metrics: Monitor perplexity drift and factuality changes after eviction adjustments.

KV cache eviction is a required control mechanism for robust long-running inference - well-designed eviction keeps serving stable without collapsing answer quality.