From c3cf754e99f315e2c52e1abb5f1a8d250ec777f9 Mon Sep 17 00:00:00 2001
From: Riverspring996 <2212442@mail.nankai.edu.cn>
Date: Thu, 26 Mar 2026 21:16:24 +0800
Subject: [PATCH] Accelerate OpenCLMmapAllocator::read() by replacing
 lseek+read syscalls with mmap-based memcpy

---
 source/backend/opencl/core/MmapPool.cpp | 18 ++++++++++--------
 source/backend/opencl/core/MmapPool.hpp | 10 ++++++++--
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/source/backend/opencl/core/MmapPool.cpp b/source/backend/opencl/core/MmapPool.cpp
index d44d36758a..3ef3b40b6f 100644
--- a/source/backend/opencl/core/MmapPool.cpp
+++ b/source/backend/opencl/core/MmapPool.cpp
@@ -41,7 +41,11 @@ std::string OpenCLMmapAllocator::onAlloc(size_t size) {
         }
         mNewMmap = true;
     }
-    mCache.insert(std::make_pair(fileName, std::make_tuple(file, size)));
+    void* mmapAddr = MNNMmapFile(file, size, false);
+    if (mmapAddr == nullptr) {
+        MNN_ERROR("MmapFile failed for %s\n", fileName.c_str());
+    }
+    mCache.insert(std::make_pair(fileName, std::make_tuple(file, size, mmapAddr)));
     mAllocTimes++;
     return fileName;
 }
@@ -52,15 +56,13 @@ bool OpenCLMmapAllocator::read(std::string fileName, size_t offset, size_t size,
         MNN_ERROR("Invalid mmap for OpenCLMmapAllocator\n");
         return false;
     }
-    file_t file = std::get<0>(iter->second);
-    auto ret = MNNSetFilePointer(file, offset);
-    if (ret != NO_ERROR) {
-        return false;
-    }
-    auto readSize = MNNReadFile(file, buffer, size);
-    if (readSize != size) {
+    void* mmapAddr = std::get<2>(iter->second);
+    if (mmapAddr == nullptr) {
+        MNN_ERROR("Mmap addr is null for %s\n", fileName.c_str());
         return false;
     }
+    memcpy(buffer, (char*)mmapAddr + offset, size);
+    return true;
 }
 bool OpenCLMmapAllocator::write(std::string fileName, size_t offset, size_t size, void* buffer){
     auto iter = mCache.find(fileName);
diff --git a/source/backend/opencl/core/MmapPool.hpp b/source/backend/opencl/core/MmapPool.hpp
index 84c79f18fb..71fd44002c 100644
--- a/source/backend/opencl/core/MmapPool.hpp
+++ b/source/backend/opencl/core/MmapPool.hpp
@@ -42,7 +42,7 @@ struct OpenCLMmapImageNode {
 
 class OpenCLMmapAllocator {
 private:
-    std::map<std::string, std::tuple<file_t, size_t>> mCache;
+    std::map<std::string, std::tuple<file_t, size_t, void*>> mCache;
     std::string mFileName;
     std::string mPrefix;
     std::string mPosfix;
@@ -54,7 +54,13 @@ class OpenCLMmapAllocator {
     OpenCLMmapAllocator(const char* dirName, const char* prefix, const char* posfix, bool autoRemove);
     ~ OpenCLMmapAllocator() {
         for (auto& iter : mCache) {
-            MNNCloseFile(std::get<0>(iter.second));
+            void*  addr = std::get<2>(iter.second);
+            size_t size = std::get<1>(iter.second);
+            file_t file = std::get<0>(iter.second);
+            if (addr != nullptr) {
+                MNNUnmapFile(addr, size);
+            }
+            MNNCloseFile(file);
             if (mRemove) {
                 MNNRemoveFile(iter.first.c_str());
             }