From 13aa3ba44fc70298339a7cba0cdbf3ec7cbc2c25 Mon Sep 17 00:00:00 2001
From: Rohan <34810284+rhn19@users.noreply.github.com>
Date: Fri, 20 Feb 2026 14:22:03 -0800
Subject: [PATCH] Fix: respect --max_seq_len for sliding window models with
 custom kv cache + sdpa

---
 optimum/exporters/executorch/integrations.py | 58 +++++++++++++++-----
 1 file changed, 43 insertions(+), 15 deletions(-)

diff --git a/optimum/exporters/executorch/integrations.py b/optimum/exporters/executorch/integrations.py
index 33cf665..32abf95 100644
--- a/optimum/exporters/executorch/integrations.py
+++ b/optimum/exporters/executorch/integrations.py
@@ -464,7 +464,10 @@ def _prepare_export_inputs(self):
             sliding_window = getattr(self.config, "sliding_window", None)
             if sliding_window is None:
                 sliding_window = self.metadata.get("sliding_window", float("inf"))
-            max_dim = min(max_seq_len, sliding_window) - 1
+            if self.use_custom_kv_cache and self.use_custom_sdpa:
+                max_dim = max_seq_len - 1
+            else:
+                max_dim = min(max_seq_len, sliding_window) - 1
             seq_len_dim = torch.export.Dim("seq_length_dim", max=max_dim)
             dynamic_shapes = {
                 "input_ids": {1: seq_len_dim},
@@ -499,22 +502,47 @@ def export(
             f"Exporting using input_ids({input_ids.shape})={input_ids}, cache_position({cache_position.shape})={cache_position}, dynamic_shapes={dynamic_shapes}, strict={strict}"
         )
 
-        exportable_module = TorchExportableModuleForDecoderOnlyLM(
-            self.model,
-        )
-        self._register_custom_attention(exportable_module)
-
-        if self.use_custom_kv_cache:
-            from optimum.executorch.attentions.custom_kv_cache import (
-                replace_with_et_custom_kv_cache,
+        max_seq_len = self.metadata.get("get_max_seq_len")
+        sliding_window = self.metadata.get("sliding_window")
+        use_ring_cache = self.use_custom_kv_cache and self.use_custom_sdpa and sliding_window is not None
+
+        if use_ring_cache:
+            from transformers.integrations.executorch import TorchExportableModuleWithHybridCache
+            from optimum.executorch.attentions.custom_kv_cache import ETCustomHybridCache
+
+            # Bypass TorchExportableModuleWithHybridCache.__init__ — it calls StaticCache which
+            # caps sliding layers to sliding_window via StaticSlidingWindowLayer, baking a
+            # <= sliding_window guard into torch.export. Instead, directly install
+            # ETCustomHybridCache sized to max_seq_len, then patch sliding layer max_cache_len
+            # so get_mask_sizes() returns max_seq_len during tracing.
+            exportable_module_inner = TorchExportableModuleWithHybridCache.__new__(TorchExportableModuleWithHybridCache)
+            torch.nn.Module.__init__(exportable_module_inner)
+            exportable_module_inner.model = self.model
+            exportable_module_inner.cache = ETCustomHybridCache(
+                config=self.model.config, max_batch_size=1, max_cache_len=max_seq_len,
+                device=self.model.device, dtype=self.model.dtype,
             )
+            for layer in exportable_module_inner.cache.layers:
+                if layer.is_sliding:
+                    layer.max_cache_len = max_seq_len
+            for i in range(len(exportable_module_inner.cache.kv_cache)):
+                exportable_module_inner.register_buffer(
+                    f"key_cache_{i}", exportable_module_inner.cache.kv_cache[i].k_cache, persistent=False)
+                exportable_module_inner.register_buffer(
+                    f"value_cache_{i}", exportable_module_inner.cache.kv_cache[i].v_cache, persistent=False)
+                if exportable_module_inner.cache.layers[i].is_sliding:
+                    exportable_module_inner.register_buffer(
+                        f"cache_positions_{i}",
+                        exportable_module_inner.cache.kv_cache[i].cache_positions_manager.cache_positions,
+                        persistent=False,
+                    )
+            exportable_module = TorchExportableModuleForDecoderOnlyLM.__new__(TorchExportableModuleForDecoderOnlyLM)
+            torch.nn.Module.__init__(exportable_module)
+            exportable_module.model = exportable_module_inner
+        else:
+            exportable_module = TorchExportableModuleForDecoderOnlyLM(self.model)
 
-            replace_with_et_custom_kv_cache(
-                exportable_module.model,
-                self.model.config,
-                self.model.generation_config,
-                self.model.dtype,
-            )
+        self._register_custom_attention(exportable_module)
 
         with torch.no_grad():
             exported_program = exportable_module.export(