diff --git a/src/os/bluestore/NVMEDevice.cc b/src/os/bluestore/NVMEDevice.cc
index bef0c635760..39446ff7a71 100644
--- a/src/os/bluestore/NVMEDevice.cc
+++ b/src/os/bluestore/NVMEDevice.cc
@@ -221,16 +221,27 @@ struct Task {
   std::function<void()> fill_cb;
   Task *next = nullptr;
   int64_t return_code;
+  Task *primary = nullptr;
   ceph::coarse_real_clock::time_point start;
-  IORequest io_request;
+  IORequest io_request = {};
   ceph::mutex lock = ceph::make_mutex("Task::lock");
   ceph::condition_variable cond;
   SharedDriverQueueData *queue = nullptr;
-  Task(NVMEDevice *dev, IOCommand c, uint64_t off, uint64_t l, int64_t rc = 0)
+  // reference count by subtasks.
+  int ref = 0;
+  Task(NVMEDevice *dev, IOCommand c, uint64_t off, uint64_t l, int64_t rc = 0,
+       Task *p = nullptr)
     : device(dev), command(c), offset(off), len(l),
-      return_code(rc),
-      start(ceph::coarse_real_clock::now()) {}
+      return_code(rc), primary(p),
+      start(ceph::coarse_real_clock::now()) {
+        if (primary) {
+          primary->ref++;
+          return_code = primary->return_code;
+        }
+     }
   ~Task() {
+    if (primary)
+      primary->ref--;
     ceph_assert(!io_request.nseg);
   }
   void release_segs(SharedDriverQueueData *queue_data) {
@@ -679,7 +690,13 @@ void io_complete(void *t, const struct spdk_nvme_cpl *completion)
       }
       delete task;
     } else {
-      task->return_code = 0;
+      if (Task* primary = task->primary; primary != nullptr) {
+        delete task;
+        if (!primary->ref)
+          primary->return_code = 0;
+      } else {
+	  task->return_code = 0;
+      }
       ctx->try_aio_wake();
     }
   } else {
@@ -791,6 +808,20 @@ void NVMEDevice::aio_submit(IOContext *ioc)
   }
 }
 
+static void ioc_append_task(IOContext *ioc, Task *t)
+{
+  Task *first, *last;
+
+  first = static_cast<Task*>(ioc->nvme_task_first);
+  last = static_cast<Task*>(ioc->nvme_task_last);
+  if (last)
+    last->next = t;
+  if (!first)
+    ioc->nvme_task_first = t;
+  ioc->nvme_task_last = t;
+  ++ioc->num_pending;
+}
+
 static void write_split(
     NVMEDevice *dev,
     uint64_t off,
@@ -798,7 +829,7 @@ static void write_split(
     IOContext *ioc)
 {
   uint64_t remain_len = bl.length(), begin = 0, write_size;
-  Task *t, *first, *last;
+  Task *t;
   // This value may need to be got from configuration later.
   uint64_t split_size = 131072; // 128KB.
 
@@ -810,18 +841,49 @@ static void write_split(
     bl.splice(0, write_size, &t->bl);
     remain_len -= write_size;
     t->ctx = ioc;
-    first = static_cast<Task*>(ioc->nvme_task_first);
-    last = static_cast<Task*>(ioc->nvme_task_last);
-    if (last)
-      last->next = t;
-    if (!first)
-      ioc->nvme_task_first = t;
-    ioc->nvme_task_last = t;
-    ++ioc->num_pending;
+    ioc_append_task(ioc, t);
     begin += write_size;
   }
 }
 
+static void make_read_tasks(
+    NVMEDevice *dev,
+    uint64_t aligned_off,
+    IOContext *ioc, char *buf, uint64_t aligned_len, Task *primary,
+    uint64_t orig_off, uint64_t orig_len)
+{
+  // This value may need to be got from configuration later.
+  uint64_t split_size = 131072; // 128KB.
+  uint64_t tmp_off = orig_off - aligned_off, remain_orig_len = orig_len;
+  auto begin = aligned_off;
+  const auto aligned_end = begin + aligned_len;
+
+  for (; begin < aligned_end; begin += split_size) {
+    auto read_size = std::min(aligned_end - begin, split_size);
+    auto tmp_len = std::min(remain_orig_len, read_size - tmp_off);
+    Task *t = nullptr;
+
+    if (primary && (aligned_len <= split_size)) {
+      t = primary;
+    } else {
+      t = new Task(dev, IOCommand::READ_COMMAND, begin, read_size, 0, primary);
+    }
+
+    t->ctx = ioc;
+
+    // TODO: if upper layer alloc memory with known physical address,
+    // we can reduce this copy
+    t->fill_cb = [buf, t, tmp_off, tmp_len]  {
+      t->copy_to_buf(buf, tmp_off, tmp_len);
+    };
+
+    ioc_append_task(ioc, t);
+    remain_orig_len -= tmp_len;
+    buf += tmp_len;
+    tmp_off = 0;
+  }
+}
+
 int NVMEDevice::aio_write(
     uint64_t off,
     bufferlist &bl,
@@ -869,14 +931,12 @@ int NVMEDevice::read(uint64_t off, uint64_t len, bufferlist *pbl,
   Task *t = new Task(this, IOCommand::READ_COMMAND, off, len, 1);
   bufferptr p = buffer::create_small_page_aligned(len);
   int r = 0;
-  t->ctx = ioc;
   char *buf = p.c_str();
-  t->fill_cb = [buf, t]() {
-    t->copy_to_buf(buf, 0, t->len);
-  };
 
-  ++ioc->num_pending;
-  ioc->nvme_task_first = t;
+  ceph_assert(ioc->nvme_task_first == nullptr);
+  ceph_assert(ioc->nvme_task_last == nullptr);
+  make_read_tasks(this, off, ioc, buf, len, t, off, len);
+  dout(5) << __func__ << " " << off << "~" << len << dendl;
   aio_submit(ioc);
   ioc->aio_wait();
 
@@ -894,26 +954,12 @@ int NVMEDevice::aio_read(
 {
   dout(20) << __func__ << " " << off << "~" << len << " ioc " << ioc << dendl;
   ceph_assert(is_valid_io(off, len));
-
-  Task *t = new Task(this, IOCommand::READ_COMMAND, off, len);
-
   bufferptr p = buffer::create_small_page_aligned(len);
   pbl->append(p);
-  t->ctx = ioc;
   char* buf = p.c_str();
-  t->fill_cb = [buf, t]() {
-    t->copy_to_buf(buf, 0, t->len);
-  };
-
-  Task *first = static_cast<Task*>(ioc->nvme_task_first);
-  Task *last = static_cast<Task*>(ioc->nvme_task_last);
-  if (last)
-    last->next = t;
-  if (!first)
-    ioc->nvme_task_first = t;
-  ioc->nvme_task_last = t;
-  ++ioc->num_pending;
 
+  make_read_tasks(this, off, ioc, buf, len, NULL, off, len);
+  dout(5) << __func__ << " " << off << "~" << len << dendl;
   return 0;
 }
 
@@ -930,13 +976,8 @@ int NVMEDevice::read_random(uint64_t off, uint64_t len, char *buf, bool buffered
   IOContext ioc(g_ceph_context, nullptr);
   Task *t = new Task(this, IOCommand::READ_COMMAND, aligned_off, aligned_len, 1);
   int r = 0;
-  t->ctx = &ioc;
-  t->fill_cb = [buf, t, off, len]() {
-    t->copy_to_buf(buf, off-t->offset, len);
-  };
 
-  ++ioc.num_pending;
-  ioc.nvme_task_first = t;
+  make_read_tasks(this, aligned_off, &ioc, buf, aligned_len, t, off, len);
   aio_submit(&ioc);
   ioc.aio_wait();