Re: [PATCH] iomap: add a swapfile activation function

[Christoph Hellwig <hch@infradead.org>]

This looks much better than using bmap, but I still think that
having the swap code build its own ineffecient extents maps is
a horible idea..

On Tue, Apr 17, 2018 at 07:50:23PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Add a new iomap_swapfile_activate function so that filesystems can
> activate swap files without having to use the obsolete and slow bmap
> function.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/iomap.c            |   99 +++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_aops.c     |   12 ++++++
>  include/linux/iomap.h |    7 +++
>  3 files changed, 118 insertions(+)
> 
> diff --git a/fs/iomap.c b/fs/iomap.c
> index afd1635..ace921b 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -1089,3 +1089,102 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(iomap_dio_rw);
> +
> +/* 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;
> +
> +	/* 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);
> +	isi->expected_page_no = page_no + nr_pages;
> +
> +	return count;
> +err:
> +	pr_err("swapon: swapfile has holes\n");
> +	return -EINVAL;
> +}
> +
> +int iomap_swapfile_activate(struct swap_info_struct *sis,
> +		struct file *swap_file, sector_t *pagespan,
> +		const struct iomap_ops *ops)
> +{
> +	struct iomap_swapfile_info isi = {
> +		.sis = sis,
> +		.lowest_ppage = (sector_t)-1ULL,
> +	};
> +	struct address_space *mapping = swap_file->f_mapping;
> +	struct inode *inode = mapping->host;
> +	loff_t pos = 0;
> +	loff_t len = i_size_read(inode);
> +	loff_t ret;
> +
> +	ret = filemap_write_and_wait(inode->i_mapping);
> +	if (ret)
> +		return ret;
> +
> +	while (len > 0) {
> +		ret = iomap_apply(inode, pos, len, IOMAP_REPORT,
> +				ops, &isi, iomap_swapfile_activate_actor);
> +		if (ret <= 0)
> +			return ret;
> +
> +		pos += ret;
> +		len -= ret;
> +	}
> +
> +	*pagespan = 1 + isi.highest_ppage - isi.lowest_ppage;
> +	sis->max = isi.expected_page_no;
> +	sis->pages = isi.expected_page_no - 1;
> +	sis->highest_bit = isi.expected_page_no - 1;
> +	return isi.nr_extents;
> +}
> +EXPORT_SYMBOL_GPL(iomap_swapfile_activate);
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 0ab824f..80de476 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1475,6 +1475,16 @@ xfs_vm_set_page_dirty(
>  	return newly_dirty;
>  }
>  
> +static int
> +xfs_iomap_swapfile_activate(
> +	struct swap_info_struct		*sis,
> +	struct file			*swap_file,
> +	sector_t			*span)
> +{
> +	sis->bdev = xfs_find_bdev_for_inode(file_inode(swap_file));
> +	return iomap_swapfile_activate(sis, swap_file, span, &xfs_iomap_ops);
> +}
> +
>  const struct address_space_operations xfs_address_space_operations = {
>  	.readpage		= xfs_vm_readpage,
>  	.readpages		= xfs_vm_readpages,
> @@ -1488,6 +1498,7 @@ const struct address_space_operations xfs_address_space_operations = {
>  	.migratepage		= buffer_migrate_page,
>  	.is_partially_uptodate  = block_is_partially_uptodate,
>  	.error_remove_page	= generic_error_remove_page,
> +	.swap_activate		= xfs_iomap_swapfile_activate,
>  };
>  
>  const struct address_space_operations xfs_dax_aops = {
> @@ -1495,4 +1506,5 @@ const struct address_space_operations xfs_dax_aops = {
>  	.direct_IO		= noop_direct_IO,
>  	.set_page_dirty		= noop_set_page_dirty,
>  	.invalidatepage		= noop_invalidatepage,
> +	.swap_activate		= xfs_iomap_swapfile_activate,
>  };
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 19a07de..66d1c35 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -106,4 +106,11 @@ typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t ret,
>  ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  		const struct iomap_ops *ops, iomap_dio_end_io_t end_io);
>  
> +struct file;
> +struct swap_info_struct;
> +
> +int iomap_swapfile_activate(struct swap_info_struct *sis,
> +		struct file *swap_file, sector_t *pagespan,
> +		const struct iomap_ops *ops);
> +
>  #endif /* LINUX_IOMAP_H */
> --
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