为什么没有调用address_space_operations writepage？

Question

我正在WrapFS中实现地址空间操作，我试图模仿现有ecryptfs文件系统源代码，因为我的目标是最终实现加密文件系统。下面给出的代码实现非常适用于readpage()，write_begin()和write_end()，但writepage()未执行，因此当我尝试通过此文件系统复制大文件时复制大约300 MB的文件后它会卡住。

static int wrapfs_writepage(struct page *page, struct writeback_control *wbc)
{
        int err = -EIO;
        struct inode *inode;
        struct inode *lower_inode;
        struct page *lower_page;
        struct address_space *lower_mapping; /* lower inode mapping */
        gfp_t mask;

        printk(KERN_INFO "in wrapfs_writepage");

        BUG_ON(!PageUptodate(page));
        inode = page->mapping->host;
        /* if no lower inode, nothing to do */
        if (!inode || !WRAPFS_I(inode) || WRAPFS_I(inode)->lower_inode) {
                err = 0;
                goto out;
        }
        lower_inode = wrapfs_lower_inode(inode);
        lower_mapping = lower_inode->i_mapping;

        mask = mapping_gfp_mask(lower_mapping) & ~(__GFP_FS);
        lower_page = find_or_create_page(lower_mapping, page->index, mask);
        if (!lower_page) {
                err = 0;
                set_page_dirty(page);
                goto out;
        }

        /* copy page data from our upper page to the lower page */
        copy_highpage(lower_page, page);
        flush_dcache_page(lower_page);
        SetPageUptodate(lower_page);
        set_page_dirty(lower_page);

        if (wbc->for_reclaim) {
                unlock_page(lower_page);
                goto out_release;
        }

        BUG_ON(!lower_mapping->a_ops->writepage);
        wait_on_page_writeback(lower_page); /* prevent multiple writers */
        clear_page_dirty_for_io(lower_page); /* emulate VFS behavior */
        err = lower_mapping->a_ops->writepage(lower_page, wbc);
        if (err < 0)
                goto out_release;

        if (err == AOP_WRITEPAGE_ACTIVATE) {
                err = 0;
                unlock_page(lower_page);
        }

out_release:
        /* b/c find_or_create_page increased refcnt */
        page_cache_release(lower_page);
out:
        /*
         * We unlock our page unconditionally, because we never return
         * AOP_WRITEPAGE_ACTIVATE.
         */
        unlock_page(page);
        return err;
}

我已正确声明了address_space_operation对象。