//代码所在文件
//zswap.c:
//代码所在函数
//static int zswap_writeback_entry(struct zpool *pool, unsigned long handle):

      /* decompress */
      dlen = PAGE_SIZE;
      src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle,
            ZPOOL_MM_RO) + sizeof(struct zswap_header);
      dst = kmap_atomic(page);
      tfm = *get_cpu_ptr(entry->pool->tfm);
      ret = crypto_comp_decompress(tfm, src, entry->length,
                    dst, &dlen);
      put_cpu_ptr(entry->pool->tfm);
      kunmap_atomic(dst);
      zpool_unmap_handle(entry->pool->zpool, entry->handle);
      BUG_ON(ret);
      BUG_ON(dlen != PAGE_SIZE);

      /* page is up to date */
      SetPageUptodate(page);
   }

   /* move it to the tail of the inactive list after end_writeback */
   SetPageReclaim(page);

   /* start writeback */
   __swap_writepage(page, &wbc, end_swap_bio_write);
   page_cache_release(page);
   zswap_written_back_pages++;