SlidingWindowCache: reduce differences to other Cache classes (#30970)

* tmp commit

* sliding window with fewer differences

* make fixup + rebase

* missing overwrite

src/transformers/cache_utils.py

@@ -829,22 +829,22 @@ class StaticCache(Cache):
             self.value_cache[layer_idx].zero_()
 
 
-class SlidingWindowCache(Cache):
+class SlidingWindowCache(StaticCache):
     """
     Sliding Window Cache class to be used with `torch.compile` for models like Mistral that support sliding window attention.
-    Every time when we try to update the cache, we compute the `indices` based on `cache_position >= self.config.sliding_window_size - 1`,
+    Every time when we try to update the cache, we compute the `indices` based on `cache_position >= self.config.sliding_window - 1`,
     if true(which means the cache can not hold all the old key value states and new states together because of the sliding window constraint),
     we need to do a cycle shift based on `indices` to replace the oldest states by the new key value states passed in.
 
-    The `to_shift` is only true once we are above sliding_window_size. Thus with `sliding_window_size==64`:
+    The `to_shift` is only true once we are above sliding_window. Thus with `sliding_window==64`:
 
-    indices = (slicing + to_shift[-1].int()-1) % self.config.sliding_window_size
+    indices = (slicing + to_shift[-1].int()-1) % self.config.sliding_window
     tensor([ 1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
         19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
         37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54,
         55, 56, 57, 58, 59, 60, 61, 62, 63,  0])
 
-    We overwrite the cache using these, then we always write at cache_position (clamped to `sliding_window_size`)
+    We overwrite the cache using these, then we always write at cache_position (clamped to `sliding_window`)
 
     Parameters:
         config (`PretrainedConfig):
@@ -866,38 +866,11 @@ class SlidingWindowCache(Cache):
                 "sliding window attention, please check if there is a `sliding_window` field in the model "
                 "config and it's not set to None."
             )
-
-        super().__init__()
-        self.max_batch_size = max_batch_size
-        # take the minimum of max_cache_len and config.sliding_window so that we allocate less memory
-        # when we do short-sentence generation
-        self.max_cache_len = config.max_position_embeddings if max_cache_len is None else max_cache_len
-        self.model_sliding_window_size = config.sliding_window
-        self.sliding_window_size = min(self.max_cache_len, self.model_sliding_window_size)
-        # Some model define a custom `head_dim` != config.hidden_size // config.num_attention_heads
-        self.head_dim = (
-            config.head_dim if hasattr(config, "head_dim") else config.hidden_size // config.num_attention_heads
-        )
-
-        self.dtype = dtype if dtype is not None else torch.float32
-        self.num_key_value_heads = (
-            config.num_attention_heads if config.num_key_value_heads is None else config.num_key_value_heads
+        max_cache_len = min(config.sliding_window, max_cache_len)
+        super().__init__(
+            config=config, max_batch_size=max_batch_size, max_cache_len=max_cache_len, device=device, dtype=dtype
         )
 
-        cache_shape = (
-            config.num_hidden_layers,
-            max_batch_size,
-            self.num_key_value_heads,
-            self.sliding_window_size,
-            self.head_dim,
-        )
-
-        self.key_cache = torch.zeros(cache_shape, dtype=self.dtype, device=device)
-        self.value_cache = torch.zeros(cache_shape, dtype=self.dtype, device=device)
-
-        torch._dynamo.mark_static_address(self.key_cache)
-        torch._dynamo.mark_static_address(self.value_cache)
-
     def update(
         self,
         key_states: torch.Tensor,
@@ -909,20 +882,21 @@ class SlidingWindowCache(Cache):
         k_out = self.key_cache[layer_idx]
         v_out = self.value_cache[layer_idx]
 
-        # assume this only happens in prefill phase when prompt length > sliding_window_size
-        if cache_position.shape[0] > self.sliding_window_size:
-            k_out = key_states[:, :, -self.sliding_window_size :, :]
-            v_out = value_states[:, :, -self.sliding_window_size :, :]
-            self.key_cache[layer_idx] = k_out
-            self.value_cache[layer_idx] = v_out
+        # assume this only happens in prefill phase when prompt length > sliding_window_size (= max_cache_len)
+        if cache_position.shape[0] > self.max_cache_len:
+            k_out = key_states[:, :, -self.max_cache_len :, :]
+            v_out = value_states[:, :, -self.max_cache_len :, :]
+            # Assumption: caches are all zeros at this point, `+=` is equivalent to `=` but compile-friendly
+            self.key_cache[layer_idx] += k_out
+            self.value_cache[layer_idx] += v_out
             # we should return the whole states instead of k_out, v_out to take the whole prompt
             # into consideration when building kv cache instead of just throwing away tokens outside of the window
             return key_states, value_states
 
-        slicing = torch.ones(self.sliding_window_size, dtype=torch.long, device=value_states.device).cumsum(0)
-        cache_position = cache_position.clamp(0, self.sliding_window_size - 1)
-        to_shift = cache_position >= self.sliding_window_size - 1
-        indices = (slicing + to_shift[-1].int() - 1) % self.sliding_window_size
+        slicing = torch.ones(self.max_cache_len, dtype=torch.long, device=value_states.device).cumsum(0)
+        cache_position = cache_position.clamp(0, self.max_cache_len - 1)
+        to_shift = cache_position >= self.max_cache_len - 1
+        indices = (slicing + to_shift[-1].int() - 1) % self.max_cache_len
 
         k_out = k_out[:, :, indices]
         v_out = v_out[:, :, indices]
@@ -930,21 +904,16 @@ class SlidingWindowCache(Cache):
         k_out[:, :, cache_position] = key_states
         v_out[:, :, cache_position] = value_states
 
-        self.key_cache[layer_idx] = k_out
-        self.value_cache[layer_idx] = v_out
+        # `_.zero()` followed by `+=` is equivalent `=`, but compile-friendly (without graph breaks due to assignment)
+        self.key_cache[layer_idx].zero_()
+        self.value_cache[layer_idx].zero_()
+
+        self.key_cache[layer_idx] += k_out
+        self.value_cache[layer_idx] += v_out
 
         return k_out, v_out
 
-    def get_seq_length(self, layer_idx: Optional[int] = 0) -> int:
-        # assume this will be called only in the first generation step
-        # `cache_postion` will be used in other cases
-        return 0
-
     def get_max_length(self) -> Optional[int]:
         # in theory there is no limit because the sliding window size is fixed
         # no matter how long the sentence is
         return None
-
-    def reset(self):
-        self.key_cache.zero_()
-        self.value_cache.zero_()

src/transformers/generation/utils.py

@@ -1368,18 +1368,15 @@ class GenerationMixin:
         Returns the resulting cache object.
         """
         cache_cls: Cache = NEED_SETUP_CACHE_CLASSES_MAPPING[cache_implementation]
+        if cache_implementation == "sliding_window":
+            max_cache_len = min(self.config.sliding_window, max_cache_len)
+
         need_new_cache = (
             not hasattr(self, "_cache")
             or (not isinstance(self._cache, cache_cls))
-            or self._cache.max_batch_size < max_batch_size
-        )
-        if cache_implementation == "sliding_window":
-            need_new_cache = need_new_cache or (
-                self._cache.sliding_window_size < self._cache.model_sliding_window_size
-                and max_cache_len > self._cache.max_cache_len
+            or self._cache.max_batch_size != max_batch_size
+            or self._cache.max_cache_len < max_cache_len
         )
-        elif cache_implementation == "static":
-            need_new_cache = need_new_cache or self._cache.max_cache_len < max_cache_len
 
         if need_new_cache:
             if hasattr(self.config, "_pre_quantization_dtype"):

src/transformers/models/mistral/modeling_mistral.py

@@ -1290,9 +1290,9 @@ class MistralForCausalLM(MistralPreTrainedModel):
             past_length > 0
             and attention_mask is not None
             and isinstance(past_key_values, SlidingWindowCache)
-            and attention_mask.shape[1] > past_key_values.sliding_window_size
+            and attention_mask.shape[1] > past_key_values.max_cache_len
         ):
-            attention_mask = attention_mask[:, -past_key_values.sliding_window_size :]
+            attention_mask = attention_mask[:, -past_key_values.max_cache_len :]
 
         # if `inputs_embeds` are passed, we only want to use them in the 1st generation step
         if inputs_embeds is not None and past_key_values is None: