linux-kernel - Re: [PATCH v5 02/11] xfs, dax: introduce xfs_dax

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Date:   Sat, 10 Mar 2018 10:46:33 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Jeff Moyer <jmoyer@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 02/11] xfs, dax: introduce xfs_dax_aops

> +int dax_set_page_dirty(struct page *page)
> +{
> +	/*
> +	 * Unlike __set_page_dirty_no_writeback that handles dirty page
> +	 * tracking in the page object, dax does all dirty tracking in
> +	 * the inode address_space in response to mkwrite faults. In the
> +	 * dax case we only need to worry about potentially dirty CPU
> +	 * caches, not dirty page cache pages to write back.
> +	 *
> +	 * This callback is defined to prevent fallback to
> +	 * __set_page_dirty_buffers() in set_page_dirty().
> +	 */
> +	return 0;
> +}

Make this a generic noop_set_page_dirty maybe?

> +EXPORT_SYMBOL(dax_set_page_dirty);
> +
> +void dax_invalidatepage(struct page *page, unsigned int offset,
> +		unsigned int length)
> +{
> +	/*
> +	 * There is no page cache to invalidate in the dax case, however
> +	 * we need this callback defined to prevent falling back to
> +	 * block_invalidatepage() in do_invalidatepage().
> +	 */
> +}

Same here.

> +EXPORT_SYMBOL(dax_invalidatepage);

And EXPORT_SYMBOL_GPL for anything dax-related, please.

> +const struct address_space_operations xfs_dax_aops = {
> +	.writepages		= xfs_vm_writepages,

Please split out the DAX case from xfs_vm_writepages.

This patch should probably also split into VFS and XFS parts.