[Bugfix] Move the _touch(computed_blocks) call in the allocate_slots …

…method to after the check for allocating new blocks.

Signed-off-by: Qianjun Zhou <[email protected]>

vllm/v1/core/kv_cache_manager.py

@@ -200,6 +200,11 @@ def allocate_slots(
             raise ValueError(
                 f"num_tokens must be greater than 0, got {num_tokens}")
 
+        num_required_blocks = cdiv(num_tokens, self.block_size)
+        if (num_required_blocks > self.free_block_queue.num_free_blocks):
+            # Cannot allocate new blocks.
+            return None
+
         # Touch the computed blocks to make sure they won't be evicted.
         if self.enable_caching:
             self._touch(computed_blocks)
@@ -208,11 +213,6 @@ def allocate_slots(
                 "Computed blocks should be empty when "
                 "prefix caching is disabled")
 
-        num_required_blocks = cdiv(num_tokens, self.block_size)
-        if (num_required_blocks > self.free_block_queue.num_free_blocks):
-            # Cannot allocate new blocks.
-            return None
-
         # Determine the number of new blocks to allocate considering
         # preallocated blocks.
         num_new_blocks = min(