fix allocation est

Signed-off-by: Cody Yu <[email protected]>

vllm/v1/core/kv_cache_manager.py

@@ -241,15 +241,25 @@ def allocate_slots(
             raise ValueError(
                 f"num_tokens must be greater than 0, got {num_tokens}")
 
+        # If a computed block is an eviction candidate (in the free queue),
+        # it cannot be counted as a free block when estimating whether we
+        # can allocate new blocks for this request.
+        num_evictable_computed_blocks = len([
+            bid for bid in computed_block_ids
+            if self.block_pool[bid].ref_cnt == 0
+        ])
+
         num_required_blocks = cdiv(num_tokens, self.block_size)
-        if num_required_blocks > self.num_free_blocks:
+        if (num_required_blocks >
+                self.num_free_blocks - num_evictable_computed_blocks):
             # Cannot allocate new blocks.
             return None
 
         # Determine the number of new blocks to allocate considering
         # preallocated blocks.
-        num_new_blocks = min(num_required_blocks + self.num_preallocate_blocks,
-                             self.num_free_blocks)
+        num_new_blocks = min(
+            num_required_blocks + self.num_preallocate_blocks,
+            self.num_free_blocks - num_evictable_computed_blocks)
         # Get the token IDs for the blocks being allocated for hashing.
         # Note that we expect this function to be called only once per
         # request, so we must have all new token IDs in the prompt.