!1891 修改代码，解决issue --- 关闭增量检查点，开启全页写，无负载情况下，create database花费25秒

Merge pull request !1891 from zhaobingyu/master

src/gausskernel/storage/buffer/bufmgr.cpp

@@ -3323,6 +3323,9 @@ static void BufferSync(int flags)
          * Header spinlock is enough to examine BM_DIRTY, see comment in
          * SyncOneBuffer.
          */
+        pg_memory_barrier();
+        buf_state = pg_atomic_read_u32(&buf_desc->state);
+        if ((buf_state & mask) == mask) {
             buf_state = LockBufHdr(buf_desc);
             if ((buf_state & mask) == mask) {
                 CkptSortItem *item = NULL;
@@ -3335,10 +3338,11 @@ static void BufferSync(int flags)
                 item->forkNum = buf_desc->tag.forkNum;
                 item->blockNum = buf_desc->tag.blockNum;
             }
-
             UnlockBufHdr(buf_desc, buf_state);
         }
 
+    }
+
     if (num_to_scan == 0) {
         gstrace_exit(GS_TRC_ID_BufferSync);
         return; /* nothing to do */