From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Sat, 21 Apr 2018 14:33:01 +0200
From: Jan Kara <jack@suse.cz>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: xfs <linux-xfs@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>, linux-mm@kvack.org
Subject: Re: [PATCH] iomap: add a swapfile activation function
Message-ID: <20180421123301.v7bbofc2joaibpi6@quack2.suse.cz>
References: <20180418025023.GM24738@magnolia>
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On Tue 17-04-18 19:50:23, Darrick J. Wong wrote:
> +
> +/* Swapfile activation */
> +
> +struct iomap_swapfile_info {
> +	struct swap_info_struct *sis;
> +	uint64_t lowest_ppage;		/* lowest physical addr seen (pages) */
> +	uint64_t highest_ppage;		/* highest physical addr seen (pages) */
> +	unsigned long expected_page_no;	/* next logical offset wanted (pages) */
> +	int nr_extents;			/* extent count */
> +};
> +
> +static loff_t iomap_swapfile_activate_actor(struct inode *inode, loff_t pos,
> +		loff_t count, void *data, struct iomap *iomap)
> +{
> +	struct iomap_swapfile_info *isi = data;
> +	unsigned long page_no = iomap->offset >> PAGE_SHIFT;
> +	unsigned long nr_pages = iomap->length >> PAGE_SHIFT;
> +	uint64_t first_ppage = iomap->addr >> PAGE_SHIFT;
> +	uint64_t last_ppage = ((iomap->addr + iomap->length) >> PAGE_SHIFT) - 1;
> +
> +	/* Only one bdev per swap file. */
> +	if (iomap->bdev != isi->sis->bdev)
> +		goto err;
> +
> +	/* Must be aligned to a page boundary. */
> +	if ((iomap->offset & ~PAGE_MASK) || (iomap->addr & ~PAGE_MASK) ||
> +	    (iomap->length & ~PAGE_MASK))
> +		goto err;

Reporting error in this case does not look equivalent to
generic_swapfile_activate()? That function just skips blocks with
insufficient alignment... And I'm actually puzzled why alignment of
physical block is needed but that's independent question.

> +	/* Only real or unwritten extents. */
> +	if (iomap->type != IOMAP_MAPPED && iomap->type != IOMAP_UNWRITTEN)
> +		goto err;
> +
> +	/* No sparse files. */
> +	if (isi->expected_page_no != page_no)
> +		goto err;
> +
> +	/* No uncommitted metadata or shared blocks or inline data. */
> +	if (iomap->flags & (IOMAP_F_DIRTY | IOMAP_F_SHARED |
> +			    IOMAP_F_DATA_INLINE))
> +		goto err;
> +
> +	/*
> +	 * Calculate how much swap space we're adding; the first page contains
> +	 * the swap header and doesn't count.
> +	 */
> +	if (page_no == 0)
> +		first_ppage++;
> +	if (isi->lowest_ppage > first_ppage)
> +		isi->lowest_ppage = first_ppage;
> +	if (isi->highest_ppage < last_ppage)
> +		isi->highest_ppage = last_ppage;
> +
> +	/* Add extent, set up for the next call. */
> +	isi->nr_extents += add_swap_extent(isi->sis, page_no, nr_pages,
> +			first_ppage);

And here add_swap_extent() can return error.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR