From 84c09913eb1458278f62f9dc393007141d3b67c3 Mon Sep 17 00:00:00 2001
From: Cheng Wan <54331508+ch-wan@users.noreply.github.com>
Date: Wed, 4 Feb 2026 02:09:55 -0800
Subject: [PATCH] Moving _alloc_extend_naive out of npu allocator (#18200)

---
 .../srt/hardware_backend/npu/allocator_npu.py | 61 ++-----------------
 python/sglang/srt/mem_cache/allocator.py      | 60 ++++++++++++++++++
 2 files changed, 65 insertions(+), 56 deletions(-)

diff --git a/python/sglang/srt/hardware_backend/npu/allocator_npu.py b/python/sglang/srt/hardware_backend/npu/allocator_npu.py
index e863de62b..01842218e 100644
--- a/python/sglang/srt/hardware_backend/npu/allocator_npu.py
+++ b/python/sglang/srt/hardware_backend/npu/allocator_npu.py
@@ -2,67 +2,16 @@ from typing import TYPE_CHECKING
 
 import torch
 
-from sglang.srt.mem_cache.allocator import PagedTokenToKVPoolAllocator
+from sglang.srt.mem_cache.allocator import (
+    PagedTokenToKVPoolAllocator,
+    alloc_extend_naive,
+)
 from sglang.srt.utils import get_num_new_pages, next_power_of_2
 
 if TYPE_CHECKING:
     from sglang.srt.mem_cache.memory_pool import KVCache
 
 
-def _alloc_extend_naive(
-    prefix_lens,
-    seq_lens,
-    last_loc,
-    free_pages,
-    out_indices,
-    page_size,
-    device,
-):
-    extend_lens = seq_lens - prefix_lens
-    end_pos = torch.cumsum(extend_lens, 0)
-    start_pos = end_pos - extend_lens
-    num_new_pages = (seq_lens + page_size - 1) // page_size - (
-        prefix_lens + page_size - 1
-    ) // page_size
-    num_full_new_pages = (seq_lens) // page_size - (
-        prefix_lens + page_size - 1
-    ) // page_size
-    need_page = num_new_pages - num_full_new_pages
-    end_new_pages = torch.cumsum(num_new_pages, 0)
-    start_new_pages = end_new_pages - num_new_pages
-    pos_in_page = torch.arange(page_size, device=device, dtype=torch.int32)
-    for i in range(len(prefix_lens)):
-        num1 = (
-            min(
-                seq_lens[i],
-                (prefix_lens[i] + page_size - 1) // page_size * page_size,
-            )
-            - prefix_lens[i]
-        )
-        if num1:
-            out_indices[start_pos[i] : start_pos[i] + num1] = (
-                last_loc[i] + 1 + pos_in_page[:num1].view(-1)
-            )
-
-        num2 = (
-            seq_lens[i] // page_size - (prefix_lens[i] + page_size - 1) // page_size
-        ) * page_size
-        if num2:
-            pages = (
-                free_pages[start_new_pages[i] : end_new_pages[i] - need_page[i]]
-                * page_size
-            )
-            out_indices[start_pos[i] + num1 : start_pos[i] + num1 + num2] = (
-                pages.view(-1, 1) + pos_in_page.view(1, -1)
-            ).view(-1)
-
-        num3 = seq_lens[i] - seq_lens[i] // page_size * page_size
-        if num3:
-            out_indices[end_pos[i] - num3 : end_pos[i]] = (
-                free_pages[end_new_pages[i] - 1] * page_size + pos_in_page[:num3]
-            ).view(-1)
-
-
 class NPUPagedTokenToKVPoolAllocator(PagedTokenToKVPoolAllocator):
     def __init__(
         self,
@@ -128,7 +77,7 @@ class NPUPagedTokenToKVPoolAllocator(PagedTokenToKVPoolAllocator):
                 dtype=torch.int32,
                 device=self.device,
             )
-            _alloc_extend_naive(
+            alloc_extend_naive(
                 prefix_lens,
                 seq_lens,
                 last_loc,
diff --git a/python/sglang/srt/mem_cache/allocator.py b/python/sglang/srt/mem_cache/allocator.py
index eaf29628b..9b6be180e 100644
--- a/python/sglang/srt/mem_cache/allocator.py
+++ b/python/sglang/srt/mem_cache/allocator.py
@@ -171,6 +171,66 @@ class TokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         return self._kvcache.load_cpu_copy(kv_cache_cpu, indices)
 
 
+def alloc_extend_naive(
+    prefix_lens,
+    seq_lens,
+    last_loc,
+    free_pages,
+    out_indices,
+    page_size,
+    device,
+):
+    extend_lens = seq_lens - prefix_lens
+    end_pos = torch.cumsum(extend_lens, 0)
+    start_pos = end_pos - extend_lens
+    num_new_pages = (seq_lens + page_size - 1) // page_size - (
+        prefix_lens + page_size - 1
+    ) // page_size
+    num_full_new_pages = (seq_lens) // page_size - (
+        prefix_lens + page_size - 1
+    ) // page_size
+    need_page = num_new_pages - num_full_new_pages
+    end_new_pages = torch.cumsum(num_new_pages, 0)
+    start_new_pages = end_new_pages - num_new_pages
+    pos_in_page = torch.arange(page_size, device=device, dtype=torch.int32)
+    for i in range(len(prefix_lens)):
+        num1 = (
+            min(
+                seq_lens[i],
+                (prefix_lens[i] + page_size - 1) // page_size * page_size,
+            )
+            - prefix_lens[i]
+        )
+        if num1:
+            out_indices[start_pos[i] : start_pos[i] + num1] = (
+                last_loc[i] + 1 + pos_in_page[:num1].view(-1)
+            )
+
+        if prefix_lens[i] + num1 == seq_lens[i]:
+            continue
+
+        num2 = (
+            seq_lens[i] // page_size - (prefix_lens[i] + page_size - 1) // page_size
+        ) * page_size
+        if num2:
+            pages = (
+                free_pages[start_new_pages[i] : end_new_pages[i] - need_page[i]]
+                * page_size
+            )
+            out_indices[start_pos[i] + num1 : start_pos[i] + num1 + num2] = (
+                pages.view(-1, 1) + pos_in_page.view(1, -1)
+            ).view(-1)
+
+        if prefix_lens[i] + num1 + num2 == seq_lens[i]:
+            continue
+
+        num3 = seq_lens[i] - seq_lens[i] // page_size * page_size
+        if num3:
+            out_indices[end_pos[i] - num3 : end_pos[i]] = (
+                free_pages[end_new_pages[i] - 1] * page_size + pos_in_page[:num3]
+            ).view(-1)
+
+
 @triton.jit
 def alloc_extend_kernel(
     pre_lens_ptr,