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Date:   Tue, 15 Oct 2019 11:40:40 -0700
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Damien Le Moal <Damien.LeMoal@wdc.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 09/12] iomap: lift the xfs writeback code to iomap
Message-ID: <20191015184040.GU13108@magnolia>
References: <20191015154345.13052-1-hch@lst.de>
 <20191015154345.13052-10-hch@lst.de>
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On Tue, Oct 15, 2019 at 05:43:42PM +0200, Christoph Hellwig wrote:
> Take the xfs writeback code and move it to fs/iomap.  A new structure
> with three methods is added as the abstraction from the generic writeback
> code to the file system.  These methods are used to map blocks, submit an
> ioend, and cancel a page that encountered an error before it was added to
> an ioend.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/buffered-io.c | 564 ++++++++++++++++++++++++++++++++++-
>  fs/iomap/trace.h       |  39 +++
>  fs/xfs/xfs_aops.c      | 662 ++++-------------------------------------
>  fs/xfs/xfs_aops.h      |  17 --
>  fs/xfs/xfs_super.c     |  11 +-
>  fs/xfs/xfs_trace.h     |  39 ---
>  include/linux/iomap.h  |  59 ++++
>  7 files changed, 722 insertions(+), 669 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index d1620c3f2a4c..00af08006cd3 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c

<snip>

> @@ -1084,3 +1091,558 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
>  	return block_page_mkwrite_return(ret);
>  }
>  EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
> +
> +static void
> +iomap_finish_page_writeback(struct inode *inode, struct bio_vec *bvec,
> +		int error)
> +{
> +	struct iomap_page *iop = to_iomap_page(bvec->bv_page);
> +
> +	if (error) {
> +		SetPageError(bvec->bv_page);
> +		mapping_set_error(inode->i_mapping, -EIO);
> +	}
> +
> +	WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE && !iop);
> +	WARN_ON_ONCE(iop && atomic_read(&iop->write_count) <= 0);
> +
> +	if (!iop || atomic_dec_and_test(&iop->write_count))
> +		end_page_writeback(bvec->bv_page);
> +}
> +
> +/*
> + * We're now finished for good with this ioend structure.  Update the page
> + * state, release holds on bios, and finally free up memory.  Do not use the
> + * ioend after this.
> + */
> +static void
> +iomap_finish_ioend(struct iomap_ioend *ioend, int error)
> +{
> +	struct inode *inode = ioend->io_inode;
> +	struct bio *bio = &ioend->io_inline_bio;
> +	struct bio *last = ioend->io_bio, *next;
> +	u64 start = bio->bi_iter.bi_sector;
> +	bool quiet = bio_flagged(bio, BIO_QUIET);
> +
> +	for (bio = &ioend->io_inline_bio; bio; bio = next) {
> +		struct bio_vec	*bvec;
> +		struct bvec_iter_all iter_all;
> +
> +		/*
> +		 * For the last bio, bi_private points to the ioend, so we
> +		 * need to explicitly end the iteration here.
> +		 */
> +		if (bio == last)
> +			next = NULL;
> +		else
> +			next = bio->bi_private;
> +
> +		/* walk each page on bio, ending page IO on them */
> +		bio_for_each_segment_all(bvec, bio, iter_all)
> +			iomap_finish_page_writeback(inode, bvec, error);
> +		bio_put(bio);
> +	}
> +
> +	if (unlikely(error && !quiet)) {
> +		printk_ratelimited(KERN_ERR
> +			"%s: writeback error on sector %llu",
> +			inode->i_sb->s_id, start);

Ugh, /this/ message.  It's pretty annoying how it doesn't tell you which
file or where in that file the write was lost.

I want to send in a patch atop your series to fix this, though I'm a
also little inclined to want to keep the message inside XFS.

Thoughts?

<snip>

> +/*
> + * Submit the bio for an ioend. We are passed an ioend with a bio attached to
> + * it, and we submit that bio. The ioend may be used for multiple bio
> + * submissions, so we only want to allocate an append transaction for the ioend
> + * once. In the case of multiple bio submission, each bio will take an IO
> + * reference to the ioend to ensure that the ioend completion is only done once
> + * all bios have been submitted and the ioend is really done.
> + *
> + * If @error is non-zero, it means that we have a situation where some part of
> + * the submission process has failed after we have marked paged for writeback
> + * and unlocked them. In this situation, we need to fail the bio and ioend
> + * rather than submit it to IO. This typically only happens on a filesystem
> + * shutdown.
> + */
> +static int
> +iomap_submit_ioend(struct iomap_writepage_ctx *wpc, struct iomap_ioend *ioend,
> +		int error)
> +{
> +	ioend->io_bio->bi_private = ioend;
> +	ioend->io_bio->bi_end_io = iomap_writepage_end_bio;
> +
> +	if (wpc->ops->submit_ioend)
> +		error = wpc->ops->submit_ioend(ioend, error);

IIRC, Brian complained about this name ^^^^^^ in a previous vesrion.

I think the documentation in the ops structure definition makes it clear
that "submit_ioend" is really a pre-submission hook.  Everyone ok with
that?

(Everything else in the patch looks ok.)

--D

> +	if (error) {
> +		/*
> +		 * If we are failing the IO now, just mark the ioend with an
> +		 * error and finish it.  This will run IO completion immediately
> +		 * as there is only one reference to the ioend at this point in
> +		 * time.
> +		 */
> +		ioend->io_bio->bi_status = errno_to_blk_status(error);
> +		bio_endio(ioend->io_bio);
> +		return error;
> +	}
> +
> +	submit_bio(ioend->io_bio);
> +	return 0;
> +}
> +
> +static struct iomap_ioend *
> +iomap_alloc_ioend(struct inode *inode, struct iomap_writepage_ctx *wpc,
> +		loff_t offset, sector_t sector, struct writeback_control *wbc)
> +{
> +	struct iomap_ioend *ioend;
> +	struct bio *bio;
> +
> +	bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, &iomap_ioend_bioset);
> +	bio_set_dev(bio, wpc->iomap.bdev);
> +	bio->bi_iter.bi_sector = sector;
> +	bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
> +	bio->bi_write_hint = inode->i_write_hint;
> +	wbc_init_bio(wbc, bio);
> +
> +	ioend = container_of(bio, struct iomap_ioend, io_inline_bio);
> +	INIT_LIST_HEAD(&ioend->io_list);
> +	ioend->io_type = wpc->iomap.type;
> +	ioend->io_flags = wpc->iomap.flags;
> +	ioend->io_inode = inode;
> +	ioend->io_size = 0;
> +	ioend->io_offset = offset;
> +	ioend->io_private = NULL;
> +	ioend->io_bio = bio;
> +	return ioend;
> +}
> +
> +/*
> + * Allocate a new bio, and chain the old bio to the new one.
> + *
> + * Note that we have to do perform the chaining in this unintuitive order
> + * so that the bi_private linkage is set up in the right direction for the
> + * traversal in iomap_finish_ioend().
> + */
> +static struct bio *
> +iomap_chain_bio(struct bio *prev)
> +{
> +	struct bio *new;
> +
> +	new = bio_alloc(GFP_NOFS, BIO_MAX_PAGES);
> +	bio_copy_dev(new, prev);/* also copies over blkcg information */
> +	new->bi_iter.bi_sector = bio_end_sector(prev);
> +	new->bi_opf = prev->bi_opf;
> +	new->bi_write_hint = prev->bi_write_hint;
> +
> +	bio_chain(prev, new);
> +	bio_get(prev);		/* for iomap_finish_ioend */
> +	submit_bio(prev);
> +	return new;
> +}
> +
> +static bool
> +iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t offset,
> +		sector_t sector)
> +{
> +	if ((wpc->iomap.flags & IOMAP_F_SHARED) !=
> +	    (wpc->ioend->io_flags & IOMAP_F_SHARED))
> +		return false;
> +	if (wpc->iomap.type != wpc->ioend->io_type)
> +		return false;
> +	if (offset != wpc->ioend->io_offset + wpc->ioend->io_size)
> +		return false;
> +	if (sector != bio_end_sector(wpc->ioend->io_bio))
> +		return false;
> +	return true;
> +}
> +
> +/*
> + * Test to see if we have an existing ioend structure that we could append to
> + * first, otherwise finish off the current ioend and start another.
> + */
> +static void
> +iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
> +		struct iomap_page *iop, struct iomap_writepage_ctx *wpc,
> +		struct writeback_control *wbc, struct list_head *iolist)
> +{
> +	sector_t sector = iomap_sector(&wpc->iomap, offset);
> +	unsigned len = i_blocksize(inode);
> +	unsigned poff = offset & (PAGE_SIZE - 1);
> +	bool merged, same_page = false;
> +
> +	if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, offset, sector)) {
> +		if (wpc->ioend)
> +			list_add(&wpc->ioend->io_list, iolist);
> +		wpc->ioend = iomap_alloc_ioend(inode, wpc, offset, sector, wbc);
> +	}
> +
> +	merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
> +			&same_page);
> +
> +	if (iop && !same_page)
> +		atomic_inc(&iop->write_count);
> +	if (!merged) {
> +		if (bio_full(wpc->ioend->io_bio, len)) {
> +			wpc->ioend->io_bio =
> +				iomap_chain_bio(wpc->ioend->io_bio);
> +		}
> +		bio_add_page(wpc->ioend->io_bio, page, len, poff);
> +	}
> +
> +	wpc->ioend->io_size += len;
> +	wbc_account_cgroup_owner(wbc, page, len);
> +}
> +
> +/*
> + * We implement an immediate ioend submission policy here to avoid needing to
> + * chain multiple ioends and hence nest mempool allocations which can violate
> + * forward progress guarantees we need to provide. The current ioend we are
> + * adding blocks to is cached on the writepage context, and if the new block
> + * does not append to the cached ioend it will create a new ioend and cache that
> + * instead.
> + *
> + * If a new ioend is created and cached, the old ioend is returned and queued
> + * locally for submission once the entire page is processed or an error has been
> + * detected.  While ioends are submitted immediately after they are completed,
> + * batching optimisations are provided by higher level block plugging.
> + *
> + * At the end of a writeback pass, there will be a cached ioend remaining on the
> + * writepage context that the caller will need to submit.
> + */
> +static int
> +iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> +		struct writeback_control *wbc, struct inode *inode,
> +		struct page *page, u64 end_offset)
> +{
> +	struct iomap_page *iop = to_iomap_page(page);
> +	struct iomap_ioend *ioend, *next;
> +	unsigned len = i_blocksize(inode);
> +	u64 file_offset; /* file offset of page */
> +	int error = 0, count = 0, i;
> +	LIST_HEAD(submit_list);
> +
> +	WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE && !iop);
> +	WARN_ON_ONCE(iop && atomic_read(&iop->write_count) != 0);
> +
> +	/*
> +	 * Walk through the page to find areas to write back. If we run off the
> +	 * end of the current map or find the current map invalid, grab a new
> +	 * one.
> +	 */
> +	for (i = 0, file_offset = page_offset(page);
> +	     i < (PAGE_SIZE >> inode->i_blkbits) && file_offset < end_offset;
> +	     i++, file_offset += len) {
> +		if (iop && !test_bit(i, iop->uptodate))
> +			continue;
> +
> +		error = wpc->ops->map_blocks(wpc, inode, file_offset);
> +		if (error)
> +			break;
> +		if (wpc->iomap.type == IOMAP_HOLE)
> +			continue;
> +		iomap_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
> +				 &submit_list);
> +		count++;
> +	}
> +
> +	WARN_ON_ONCE(!wpc->ioend && !list_empty(&submit_list));
> +	WARN_ON_ONCE(!PageLocked(page));
> +	WARN_ON_ONCE(PageWriteback(page));
> +
> +	/*
> +	 * On error, we have to fail the ioend here because we may have set
> +	 * pages under writeback, we have to make sure we run IO completion to
> +	 * mark the error state of the IO appropriately, so we can't cancel the
> +	 * ioend directly here.  That means we have to mark this page as under
> +	 * writeback if we included any blocks from it in the ioend chain so
> +	 * that completion treats it correctly.
> +	 *
> +	 * If we didn't include the page in the ioend, the on error we can
> +	 * simply discard and unlock it as there are no other users of the page
> +	 * now.  The caller will still need to trigger submission of outstanding
> +	 * ioends on the writepage context so they are treated correctly on
> +	 * error.
> +	 */
> +	if (unlikely(error)) {
> +		if (!count) {
> +			if (wpc->ops->discard_page)
> +				wpc->ops->discard_page(page);
> +			ClearPageUptodate(page);
> +			unlock_page(page);
> +			goto done;
> +		}
> +
> +		/*
> +		 * If the page was not fully cleaned, we need to ensure that the
> +		 * higher layers come back to it correctly.  That means we need
> +		 * to keep the page dirty, and for WB_SYNC_ALL writeback we need
> +		 * to ensure the PAGECACHE_TAG_TOWRITE index mark is not removed
> +		 * so another attempt to write this page in this writeback sweep
> +		 * will be made.
> +		 */
> +		set_page_writeback_keepwrite(page);
> +	} else {
> +		clear_page_dirty_for_io(page);
> +		set_page_writeback(page);
> +	}
> +
> +	unlock_page(page);
> +
> +	/*
> +	 * Preserve the original error if there was one, otherwise catch
> +	 * submission errors here and propagate into subsequent ioend
> +	 * submissions.
> +	 */
> +	list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
> +		int error2;
> +
> +		list_del_init(&ioend->io_list);
> +		error2 = iomap_submit_ioend(wpc, ioend, error);
> +		if (error2 && !error)
> +			error = error2;
> +	}
> +
> +	/*
> +	 * We can end up here with no error and nothing to write only if we race
> +	 * with a partial page truncate on a sub-page block sized filesystem.
> +	 */
> +	if (!count)
> +		end_page_writeback(page);
> +done:
> +	mapping_set_error(page->mapping, error);
> +	return error;
> +}
> +
> +/*
> + * Write out a dirty page.
> + *
> + * For delalloc space on the page we need to allocate space and flush it.
> + * For unwritten space on the page we need to start the conversion to
> + * regular allocated space.
> + */
> +static int
> +iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> +{
> +	struct iomap_writepage_ctx *wpc = data;
> +	struct inode *inode = page->mapping->host;
> +	pgoff_t end_index;
> +	u64 end_offset;
> +	loff_t offset;
> +
> +	trace_iomap_writepage(inode, page, 0, 0);
> +
> +	/*
> +	 * Refuse to write the page out if we are called from reclaim context.
> +	 *
> +	 * This avoids stack overflows when called from deeply used stacks in
> +	 * random callers for direct reclaim or memcg reclaim.  We explicitly
> +	 * allow reclaim from kswapd as the stack usage there is relatively low.
> +	 *
> +	 * This should never happen except in the case of a VM regression so
> +	 * warn about it.
> +	 */
> +	if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> +			PF_MEMALLOC))
> +		goto redirty;
> +
> +	/*
> +	 * Given that we do not allow direct reclaim to call us, we should
> +	 * never be called while in a filesystem transaction.
> +	 */
> +	if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> +		goto redirty;
> +
> +	/*
> +	 * Is this page beyond the end of the file?
> +	 *
> +	 * The page index is less than the end_index, adjust the end_offset
> +	 * to the highest offset that this page should represent.
> +	 * -----------------------------------------------------
> +	 * |			file mapping	       | <EOF> |
> +	 * -----------------------------------------------------
> +	 * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
> +	 * ^--------------------------------^----------|--------
> +	 * |     desired writeback range    |      see else    |
> +	 * ---------------------------------^------------------|
> +	 */
> +	offset = i_size_read(inode);
> +	end_index = offset >> PAGE_SHIFT;
> +	if (page->index < end_index)
> +		end_offset = (loff_t)(page->index + 1) << PAGE_SHIFT;
> +	else {
> +		/*
> +		 * Check whether the page to write out is beyond or straddles
> +		 * i_size or not.
> +		 * -------------------------------------------------------
> +		 * |		file mapping		        | <EOF>  |
> +		 * -------------------------------------------------------
> +		 * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
> +		 * ^--------------------------------^-----------|---------
> +		 * |				    |      Straddles     |
> +		 * ---------------------------------^-----------|--------|
> +		 */
> +		unsigned offset_into_page = offset & (PAGE_SIZE - 1);
> +
> +		/*
> +		 * Skip the page if it is fully outside i_size, e.g. due to a
> +		 * truncate operation that is in progress. We must redirty the
> +		 * page so that reclaim stops reclaiming it. Otherwise
> +		 * iomap_vm_releasepage() is called on it and gets confused.
> +		 *
> +		 * Note that the end_index is unsigned long, it would overflow
> +		 * if the given offset is greater than 16TB on 32-bit system
> +		 * and if we do check the page is fully outside i_size or not
> +		 * via "if (page->index >= end_index + 1)" as "end_index + 1"
> +		 * will be evaluated to 0.  Hence this page will be redirtied
> +		 * and be written out repeatedly which would result in an
> +		 * infinite loop, the user program that perform this operation
> +		 * will hang.  Instead, we can verify this situation by checking
> +		 * if the page to write is totally beyond the i_size or if it's
> +		 * offset is just equal to the EOF.
> +		 */
> +		if (page->index > end_index ||
> +		    (page->index == end_index && offset_into_page == 0))
> +			goto redirty;
> +
> +		/*
> +		 * The page straddles i_size.  It must be zeroed out on each
> +		 * and every writepage invocation because it may be mmapped.
> +		 * "A file is mapped in multiples of the page size.  For a file
> +		 * that is not a multiple of the page size, the remaining
> +		 * memory is zeroed when mapped, and writes to that region are
> +		 * not written out to the file."
> +		 */
> +		zero_user_segment(page, offset_into_page, PAGE_SIZE);
> +
> +		/* Adjust the end_offset to the end of file */
> +		end_offset = offset;
> +	}
> +
> +	return iomap_writepage_map(wpc, wbc, inode, page, end_offset);
> +
> +redirty:
> +	redirty_page_for_writepage(wbc, page);
> +	unlock_page(page);
> +	return 0;
> +}
> +
> +int
> +iomap_writepage(struct page *page, struct writeback_control *wbc,
> +		struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops)
> +{
> +	int ret;
> +
> +	wpc->ops = ops;
> +	ret = iomap_do_writepage(page, wbc, wpc);
> +	if (!wpc->ioend)
> +		return ret;
> +	return iomap_submit_ioend(wpc, wpc->ioend, ret);
> +}
> +EXPORT_SYMBOL_GPL(iomap_writepage);
> +
> +int
> +iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
> +		struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops)
> +{
> +	int			ret;
> +
> +	wpc->ops = ops;
> +	ret = write_cache_pages(mapping, wbc, iomap_do_writepage, wpc);
> +	if (!wpc->ioend)
> +		return ret;
> +	return iomap_submit_ioend(wpc, wpc->ioend, ret);
> +}
> +EXPORT_SYMBOL_GPL(iomap_writepages);
> +
> +static int __init iomap_init(void)
> +{
> +	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> +			   offsetof(struct iomap_ioend, io_inline_bio),
> +			   BIOSET_NEED_BVECS);
> +}
> +fs_initcall(iomap_init);
> diff --git a/fs/iomap/trace.h b/fs/iomap/trace.h
> index 3900de1d871d..3bc8d0263020 100644
> --- a/fs/iomap/trace.h
> +++ b/fs/iomap/trace.h
> @@ -41,6 +41,45 @@ DEFINE_EVENT(iomap_readpage_class, name,	\
>  DEFINE_READPAGE_EVENT(iomap_readpage);
>  DEFINE_READPAGE_EVENT(iomap_readpages);
>  
> +DECLARE_EVENT_CLASS(iomap_page_class,
> +	TP_PROTO(struct inode *inode, struct page *page, unsigned long off,
> +		 unsigned int len),
> +	TP_ARGS(inode, page, off, len),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(u64, ino)
> +		__field(pgoff_t, pgoff)
> +		__field(loff_t, size)
> +		__field(unsigned long, offset)
> +		__field(unsigned int, length)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = inode->i_sb->s_dev;
> +		__entry->ino = inode->i_ino;
> +		__entry->pgoff = page_offset(page);
> +		__entry->size = i_size_read(inode);
> +		__entry->offset = off;
> +		__entry->length = len;
> +	),
> +	TP_printk("dev %d:%d ino 0x%llx pgoff 0x%lx size 0x%llx offset %lx "
> +		  "length %x",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  __entry->ino,
> +		  __entry->pgoff,
> +		  __entry->size,
> +		  __entry->offset,
> +		  __entry->length)
> +)
> +
> +#define DEFINE_PAGE_EVENT(name)		\
> +DEFINE_EVENT(iomap_page_class, name,	\
> +	TP_PROTO(struct inode *inode, struct page *page, unsigned long off, \
> +		 unsigned int len),	\
> +	TP_ARGS(inode, page, off, len))
> +DEFINE_PAGE_EVENT(iomap_writepage);
> +DEFINE_PAGE_EVENT(iomap_releasepage);
> +DEFINE_PAGE_EVENT(iomap_invalidatepage);
> +
>  #endif /* _IOMAP_TRACE_H */
>  
>  #undef TRACE_INCLUDE_PATH
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index e2033b070f4a..546bd8a48cad 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -18,16 +18,18 @@
>  #include "xfs_bmap_util.h"
>  #include "xfs_reflink.h"
>  
> -/*
> - * structure owned by writepages passed to individual writepage calls
> - */
>  struct xfs_writepage_ctx {
> -	struct iomap		iomap;
> +	struct iomap_writepage_ctx ctx;
>  	unsigned int		data_seq;
>  	unsigned int		cow_seq;
> -	struct xfs_ioend	*ioend;
>  };
>  
> +static inline struct xfs_writepage_ctx *
> +XFS_WPC(struct iomap_writepage_ctx *ctx)
> +{
> +	return container_of(ctx, struct xfs_writepage_ctx, ctx);
> +}
> +
>  struct block_device *
>  xfs_find_bdev_for_inode(
>  	struct inode		*inode)
> @@ -54,87 +56,10 @@ xfs_find_daxdev_for_inode(
>  		return mp->m_ddev_targp->bt_daxdev;
>  }
>  
> -static void
> -xfs_finish_page_writeback(
> -	struct inode		*inode,
> -	struct bio_vec	*bvec,
> -	int			error)
> -{
> -	struct iomap_page	*iop = to_iomap_page(bvec->bv_page);
> -
> -	if (error) {
> -		SetPageError(bvec->bv_page);
> -		mapping_set_error(inode->i_mapping, -EIO);
> -	}
> -
> -	ASSERT(iop || i_blocksize(inode) == PAGE_SIZE);
> -	ASSERT(!iop || atomic_read(&iop->write_count) > 0);
> -
> -	if (!iop || atomic_dec_and_test(&iop->write_count))
> -		end_page_writeback(bvec->bv_page);
> -}
> -
> -/*
> - * We're now finished for good with this ioend structure.  Update the page
> - * state, release holds on bios, and finally free up memory.  Do not use the
> - * ioend after this.
> - */
> -STATIC void
> -xfs_destroy_ioend(
> -	struct xfs_ioend	*ioend,
> -	int			error)
> -{
> -	struct inode		*inode = ioend->io_inode;
> -	struct bio		*bio = &ioend->io_inline_bio;
> -	struct bio		*last = ioend->io_bio, *next;
> -	u64			start = bio->bi_iter.bi_sector;
> -	bool			quiet = bio_flagged(bio, BIO_QUIET);
> -
> -	for (bio = &ioend->io_inline_bio; bio; bio = next) {
> -		struct bio_vec	*bvec;
> -		struct bvec_iter_all iter_all;
> -
> -		/*
> -		 * For the last bio, bi_private points to the ioend, so we
> -		 * need to explicitly end the iteration here.
> -		 */
> -		if (bio == last)
> -			next = NULL;
> -		else
> -			next = bio->bi_private;
> -
> -		/* walk each page on bio, ending page IO on them */
> -		bio_for_each_segment_all(bvec, bio, iter_all)
> -			xfs_finish_page_writeback(inode, bvec, error);
> -		bio_put(bio);
> -	}
> -
> -	if (unlikely(error && !quiet)) {
> -		xfs_err_ratelimited(XFS_I(inode)->i_mount,
> -			"writeback error on sector %llu", start);
> -	}
> -}
> -
> -static void
> -xfs_destroy_ioends(
> -	struct xfs_ioend	*ioend,
> -	int			error)
> -{
> -	struct list_head	tmp;
> -
> -	list_replace_init(&ioend->io_list, &tmp);
> -	xfs_destroy_ioend(ioend, error);
> -	while ((ioend = list_first_entry_or_null(&tmp, struct xfs_ioend,
> -			io_list))) {
> -		list_del_init(&ioend->io_list);
> -		xfs_destroy_ioend(ioend, error);
> -	}
> -}
> -
>  /*
>   * Fast and loose check if this write could update the on-disk inode size.
>   */
> -static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
> +static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
>  {
>  	return ioend->io_offset + ioend->io_size >
>  		XFS_I(ioend->io_inode)->i_d.di_size;
> @@ -142,7 +67,7 @@ static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
>  
>  STATIC int
>  xfs_setfilesize_trans_alloc(
> -	struct xfs_ioend	*ioend)
> +	struct iomap_ioend	*ioend)
>  {
>  	struct xfs_mount	*mp = XFS_I(ioend->io_inode)->i_mount;
>  	struct xfs_trans	*tp;
> @@ -215,7 +140,7 @@ xfs_setfilesize(
>  
>  STATIC int
>  xfs_setfilesize_ioend(
> -	struct xfs_ioend	*ioend,
> +	struct iomap_ioend	*ioend,
>  	int			error)
>  {
>  	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
> @@ -243,7 +168,7 @@ xfs_setfilesize_ioend(
>   */
>  STATIC void
>  xfs_end_ioend(
> -	struct xfs_ioend	*ioend)
> +	struct iomap_ioend	*ioend)
>  {
>  	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
>  	xfs_off_t		offset = ioend->io_offset;
> @@ -289,31 +214,10 @@ xfs_end_ioend(
>  done:
>  	if (ioend->io_private)
>  		error = xfs_setfilesize_ioend(ioend, error);
> -	xfs_destroy_ioends(ioend, error);
> +	iomap_finish_ioends(ioend, error);
>  	memalloc_nofs_restore(nofs_flag);
>  }
>  
> -/*
> - * We can merge two adjacent ioends if they have the same set of work to do.
> - */
> -static bool
> -xfs_ioend_can_merge(
> -	struct xfs_ioend	*ioend,
> -	struct xfs_ioend	*next)
> -{
> -	if (ioend->io_bio->bi_status != next->io_bio->bi_status)
> -		return false;
> -	if ((ioend->io_flags & IOMAP_F_SHARED) ^
> -	    (next->io_flags & IOMAP_F_SHARED))
> -		return false;
> -	if ((ioend->io_type == IOMAP_UNWRITTEN) ^
> -	    (next->io_type == IOMAP_UNWRITTEN))
> -		return false;
> -	if (ioend->io_offset + ioend->io_size != next->io_offset)
> -		return false;
> -	return true;
> -}
> -
>  /*
>   * If the to be merged ioend has a preallocated transaction for file
>   * size updates we need to ensure the ioend it is merged into also
> @@ -322,8 +226,8 @@ xfs_ioend_can_merge(
>   */
>  static void
>  xfs_ioend_merge_private(
> -	struct xfs_ioend	*ioend,
> -	struct xfs_ioend	*next)
> +	struct iomap_ioend	*ioend,
> +	struct iomap_ioend	*next)
>  {
>  	if (!ioend->io_private) {
>  		ioend->io_private = next->io_private;
> @@ -333,53 +237,6 @@ xfs_ioend_merge_private(
>  	}
>  }
>  
> -/* Try to merge adjacent completions. */
> -STATIC void
> -xfs_ioend_try_merge(
> -	struct xfs_ioend	*ioend,
> -	struct list_head	*more_ioends)
> -{
> -	struct xfs_ioend	*next;
> -
> -	INIT_LIST_HEAD(&ioend->io_list);
> -
> -	while ((next = list_first_entry_or_null(more_ioends, struct xfs_ioend,
> -			io_list))) {
> -		if (!xfs_ioend_can_merge(ioend, next))
> -			break;
> -		list_move_tail(&next->io_list, &ioend->io_list);
> -		ioend->io_size += next->io_size;
> -		if (next->io_private)
> -			xfs_ioend_merge_private(ioend, next);
> -	}
> -}
> -
> -/* list_sort compare function for ioends */
> -static int
> -xfs_ioend_compare(
> -	void			*priv,
> -	struct list_head	*a,
> -	struct list_head	*b)
> -{
> -	struct xfs_ioend	*ia;
> -	struct xfs_ioend	*ib;
> -
> -	ia = container_of(a, struct xfs_ioend, io_list);
> -	ib = container_of(b, struct xfs_ioend, io_list);
> -	if (ia->io_offset < ib->io_offset)
> -		return -1;
> -	else if (ia->io_offset > ib->io_offset)
> -		return 1;
> -	return 0;
> -}
> -
> -static void
> -xfs_sort_ioends(
> -	struct list_head	*ioend_list)
> -{
> -	list_sort(NULL, ioend_list, xfs_ioend_compare);
> -}
> -
>  /* Finish all pending io completions. */
>  void
>  xfs_end_io(
> @@ -387,7 +244,7 @@ xfs_end_io(
>  {
>  	struct xfs_inode	*ip =
>  		container_of(work, struct xfs_inode, i_ioend_work);
> -	struct xfs_ioend	*ioend;
> +	struct iomap_ioend	*ioend;
>  	struct list_head	tmp;
>  	unsigned long		flags;
>  
> @@ -395,16 +252,16 @@ xfs_end_io(
>  	list_replace_init(&ip->i_ioend_list, &tmp);
>  	spin_unlock_irqrestore(&ip->i_ioend_lock, flags);
>  
> -	xfs_sort_ioends(&tmp);
> -	while ((ioend = list_first_entry_or_null(&tmp, struct xfs_ioend,
> +	iomap_sort_ioends(&tmp);
> +	while ((ioend = list_first_entry_or_null(&tmp, struct iomap_ioend,
>  			io_list))) {
>  		list_del_init(&ioend->io_list);
> -		xfs_ioend_try_merge(ioend, &tmp);
> +		iomap_ioend_try_merge(ioend, &tmp, xfs_ioend_merge_private);
>  		xfs_end_ioend(ioend);
>  	}
>  }
>  
> -static inline bool xfs_ioend_needs_workqueue(struct xfs_ioend *ioend)
> +static inline bool xfs_ioend_needs_workqueue(struct iomap_ioend *ioend)
>  {
>  	return ioend->io_private ||
>  		ioend->io_type == IOMAP_UNWRITTEN ||
> @@ -415,20 +272,18 @@ STATIC void
>  xfs_end_bio(
>  	struct bio		*bio)
>  {
> -	struct xfs_ioend	*ioend = bio->bi_private;
> +	struct iomap_ioend	*ioend = bio->bi_private;
>  	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
> -	struct xfs_mount	*mp = ip->i_mount;
>  	unsigned long		flags;
>  
> -	if (xfs_ioend_needs_workqueue(ioend)) {
> -		spin_lock_irqsave(&ip->i_ioend_lock, flags);
> -		if (list_empty(&ip->i_ioend_list))
> -			WARN_ON_ONCE(!queue_work(mp->m_unwritten_workqueue,
> -						 &ip->i_ioend_work));
> -		list_add_tail(&ioend->io_list, &ip->i_ioend_list);
> -		spin_unlock_irqrestore(&ip->i_ioend_lock, flags);
> -	} else
> -		xfs_destroy_ioend(ioend, blk_status_to_errno(bio->bi_status));
> +	ASSERT(xfs_ioend_needs_workqueue(ioend));
> +
> +	spin_lock_irqsave(&ip->i_ioend_lock, flags);
> +	if (list_empty(&ip->i_ioend_list))
> +		WARN_ON_ONCE(!queue_work(ip->i_mount->m_unwritten_workqueue,
> +					 &ip->i_ioend_work));
> +	list_add_tail(&ioend->io_list, &ip->i_ioend_list);
> +	spin_unlock_irqrestore(&ip->i_ioend_lock, flags);
>  }
>  
>  /*
> @@ -437,7 +292,7 @@ xfs_end_bio(
>   */
>  static bool
>  xfs_imap_valid(
> -	struct xfs_writepage_ctx	*wpc,
> +	struct iomap_writepage_ctx	*wpc,
>  	struct xfs_inode		*ip,
>  	loff_t				offset)
>  {
> @@ -459,10 +314,10 @@ xfs_imap_valid(
>  	 * checked (and found nothing at this offset) could have added
>  	 * overlapping blocks.
>  	 */
> -	if (wpc->data_seq != READ_ONCE(ip->i_df.if_seq))
> +	if (XFS_WPC(wpc)->data_seq != READ_ONCE(ip->i_df.if_seq))
>  		return false;
>  	if (xfs_inode_has_cow_data(ip) &&
> -	    wpc->cow_seq != READ_ONCE(ip->i_cowfp->if_seq))
> +	    XFS_WPC(wpc)->cow_seq != READ_ONCE(ip->i_cowfp->if_seq))
>  		return false;
>  	return true;
>  }
> @@ -477,12 +332,18 @@ xfs_imap_valid(
>   */
>  static int
>  xfs_convert_blocks(
> -	struct xfs_writepage_ctx *wpc,
> +	struct iomap_writepage_ctx *wpc,
>  	struct xfs_inode	*ip,
>  	int			whichfork,
>  	loff_t			offset)
>  {
>  	int			error;
> +	unsigned		*seq;
> +
> +	if (whichfork == XFS_COW_FORK)
> +		seq = &XFS_WPC(wpc)->cow_seq;
> +	else
> +		seq = &XFS_WPC(wpc)->data_seq;
>  
>  	/*
>  	 * Attempt to allocate whatever delalloc extent currently backs offset
> @@ -492,8 +353,7 @@ xfs_convert_blocks(
>  	 */
>  	do {
>  		error = xfs_bmapi_convert_delalloc(ip, whichfork, offset,
> -				&wpc->iomap, whichfork == XFS_COW_FORK ?
> -					&wpc->cow_seq : &wpc->data_seq);
> +				&wpc->iomap, seq);
>  		if (error)
>  			return error;
>  	} while (wpc->iomap.offset + wpc->iomap.length <= offset);
> @@ -501,9 +361,9 @@ xfs_convert_blocks(
>  	return 0;
>  }
>  
> -STATIC int
> +static int
>  xfs_map_blocks(
> -	struct xfs_writepage_ctx *wpc,
> +	struct iomap_writepage_ctx *wpc,
>  	struct inode		*inode,
>  	loff_t			offset)
>  {
> @@ -559,7 +419,7 @@ xfs_map_blocks(
>  	    xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap))
>  		cow_fsb = imap.br_startoff;
>  	if (cow_fsb != NULLFILEOFF && cow_fsb <= offset_fsb) {
> -		wpc->cow_seq = READ_ONCE(ip->i_cowfp->if_seq);
> +		XFS_WPC(wpc)->cow_seq = READ_ONCE(ip->i_cowfp->if_seq);
>  		xfs_iunlock(ip, XFS_ILOCK_SHARED);
>  
>  		whichfork = XFS_COW_FORK;
> @@ -582,7 +442,7 @@ xfs_map_blocks(
>  	 */
>  	if (!xfs_iext_lookup_extent(ip, &ip->i_df, offset_fsb, &icur, &imap))
>  		imap.br_startoff = end_fsb;	/* fake a hole past EOF */
> -	wpc->data_seq = READ_ONCE(ip->i_df.if_seq);
> +	XFS_WPC(wpc)->data_seq = READ_ONCE(ip->i_df.if_seq);
>  	xfs_iunlock(ip, XFS_ILOCK_SHARED);
>  
>  	/* landed in a hole or beyond EOF? */
> @@ -645,24 +505,9 @@ xfs_map_blocks(
>  	return 0;
>  }
>  
> -/*
> - * Submit the bio for an ioend. We are passed an ioend with a bio attached to
> - * it, and we submit that bio. The ioend may be used for multiple bio
> - * submissions, so we only want to allocate an append transaction for the ioend
> - * once. In the case of multiple bio submission, each bio will take an IO
> - * reference to the ioend to ensure that the ioend completion is only done once
> - * all bios have been submitted and the ioend is really done.
> - *
> - * If @status is non-zero, it means that we have a situation where some part of
> - * the submission process has failed after we have marked paged for writeback
> - * and unlocked them. In this situation, we need to fail the bio and ioend
> - * rather than submit it to IO. This typically only happens on a filesystem
> - * shutdown.
> - */
> -STATIC int
> +static int
>  xfs_submit_ioend(
> -	struct writeback_control *wbc,
> -	struct xfs_ioend	*ioend,
> +	struct iomap_ioend	*ioend,
>  	int			status)
>  {
>  	unsigned int		nofs_flag;
> @@ -690,147 +535,9 @@ xfs_submit_ioend(
>  
>  	memalloc_nofs_restore(nofs_flag);
>  
> -	ioend->io_bio->bi_private = ioend;
> -	ioend->io_bio->bi_end_io = xfs_end_bio;
> -
> -	/*
> -	 * If we are failing the IO now, just mark the ioend with an
> -	 * error and finish it. This will run IO completion immediately
> -	 * as there is only one reference to the ioend at this point in
> -	 * time.
> -	 */
> -	if (status) {
> -		ioend->io_bio->bi_status = errno_to_blk_status(status);
> -		bio_endio(ioend->io_bio);
> -		return status;
> -	}
> -
> -	submit_bio(ioend->io_bio);
> -	return 0;
> -}
> -
> -static struct xfs_ioend *
> -xfs_alloc_ioend(
> -	struct inode		*inode,
> -	struct xfs_writepage_ctx *wpc,
> -	xfs_off_t		offset,
> -	sector_t		sector,
> -	struct writeback_control *wbc)
> -{
> -	struct xfs_ioend	*ioend;
> -	struct bio		*bio;
> -
> -	bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, &xfs_ioend_bioset);
> -	bio_set_dev(bio, wpc->iomap.bdev);
> -	bio->bi_iter.bi_sector = sector;
> -	bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
> -	bio->bi_write_hint = inode->i_write_hint;
> -	wbc_init_bio(wbc, bio);
> -
> -	ioend = container_of(bio, struct xfs_ioend, io_inline_bio);
> -	INIT_LIST_HEAD(&ioend->io_list);
> -	ioend->io_type = wpc->iomap.type;
> -	ioend->io_flags = wpc->iomap.flags;
> -	ioend->io_inode = inode;
> -	ioend->io_size = 0;
> -	ioend->io_offset = offset;
> -	ioend->io_private = NULL;
> -	ioend->io_bio = bio;
> -	return ioend;
> -}
> -
> -/*
> - * Allocate a new bio, and chain the old bio to the new one.
> - *
> - * Note that we have to do perform the chaining in this unintuitive order
> - * so that the bi_private linkage is set up in the right direction for the
> - * traversal in xfs_destroy_ioend().
> - */
> -static struct bio *
> -xfs_chain_bio(
> -	struct bio		*prev)
> -{
> -	struct bio *new;
> -
> -	new = bio_alloc(GFP_NOFS, BIO_MAX_PAGES);
> -	bio_copy_dev(new, prev);/* also copies over blkcg information */
> -	new->bi_iter.bi_sector = bio_end_sector(prev);
> -	new->bi_opf = prev->bi_opf;
> -	new->bi_write_hint = prev->bi_write_hint;
> -
> -	bio_chain(prev, new);
> -	bio_get(prev);		/* for xfs_destroy_ioend */
> -	submit_bio(prev);
> -	return new;
> -}
> -
> -static bool
> -xfs_can_add_to_ioend(
> -	struct xfs_writepage_ctx *wpc,
> -	xfs_off_t		offset,
> -	sector_t		sector)
> -{
> -	if ((wpc->iomap.flags & IOMAP_F_SHARED) !=
> -	    (wpc->ioend->io_flags & IOMAP_F_SHARED))
> -		return false;
> -	if (wpc->iomap.type != wpc->ioend->io_type)
> -		return false;
> -	if (offset != wpc->ioend->io_offset + wpc->ioend->io_size)
> -		return false;
> -	if (sector != bio_end_sector(wpc->ioend->io_bio))
> -		return false;
> -	return true;
> -}
> -
> -/*
> - * Test to see if we have an existing ioend structure that we could append to
> - * first, otherwise finish off the current ioend and start another.
> - */
> -STATIC void
> -xfs_add_to_ioend(
> -	struct inode		*inode,
> -	xfs_off_t		offset,
> -	struct page		*page,
> -	struct iomap_page	*iop,
> -	struct xfs_writepage_ctx *wpc,
> -	struct writeback_control *wbc,
> -	struct list_head	*iolist)
> -{
> -	sector_t		sector = iomap_sector(&wpc->iomap, offset);
> -	unsigned		len = i_blocksize(inode);
> -	unsigned		poff = offset & (PAGE_SIZE - 1);
> -	bool			merged, same_page = false;
> -
> -	if (!wpc->ioend || !xfs_can_add_to_ioend(wpc, offset, sector)) {
> -		if (wpc->ioend)
> -			list_add(&wpc->ioend->io_list, iolist);
> -		wpc->ioend = xfs_alloc_ioend(inode, wpc, offset, sector, wbc);
> -	}
> -
> -	merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
> -			&same_page);
> -
> -	if (iop && !same_page)
> -		atomic_inc(&iop->write_count);
> -
> -	if (!merged) {
> -		if (bio_full(wpc->ioend->io_bio, len))
> -			wpc->ioend->io_bio = xfs_chain_bio(wpc->ioend->io_bio);
> -		bio_add_page(wpc->ioend->io_bio, page, len, poff);
> -	}
> -
> -	wpc->ioend->io_size += len;
> -	wbc_account_cgroup_owner(wbc, page, len);
> -}
> -
> -STATIC void
> -xfs_vm_invalidatepage(
> -	struct page		*page,
> -	unsigned int		offset,
> -	unsigned int		length)
> -{
> -	trace_xfs_invalidatepage(page->mapping->host, page, offset, length);
> -	iomap_invalidatepage(page, offset, length);
> +	if (xfs_ioend_needs_workqueue(ioend))
> +		ioend->io_bio->bi_end_io = xfs_end_bio;
> +	return status;
>  }
>  
>  /*
> @@ -844,8 +551,8 @@ xfs_vm_invalidatepage(
>   * transaction as there is no space left for block reservation (typically why we
>   * see a ENOSPC in writeback).
>   */
> -STATIC void
> -xfs_aops_discard_page(
> +static void
> +xfs_discard_page(
>  	struct page		*page)
>  {
>  	struct inode		*inode = page->mapping->host;
> @@ -867,246 +574,14 @@ xfs_aops_discard_page(
>  	if (error && !XFS_FORCED_SHUTDOWN(mp))
>  		xfs_alert(mp, "page discard unable to remove delalloc mapping.");
>  out_invalidate:
> -	xfs_vm_invalidatepage(page, 0, PAGE_SIZE);
> +	iomap_invalidatepage(page, 0, PAGE_SIZE);
>  }
>  
> -/*
> - * We implement an immediate ioend submission policy here to avoid needing to
> - * chain multiple ioends and hence nest mempool allocations which can violate
> - * forward progress guarantees we need to provide. The current ioend we are
> - * adding blocks to is cached on the writepage context, and if the new block
> - * does not append to the cached ioend it will create a new ioend and cache that
> - * instead.
> - *
> - * If a new ioend is created and cached, the old ioend is returned and queued
> - * locally for submission once the entire page is processed or an error has been
> - * detected.  While ioends are submitted immediately after they are completed,
> - * batching optimisations are provided by higher level block plugging.
> - *
> - * At the end of a writeback pass, there will be a cached ioend remaining on the
> - * writepage context that the caller will need to submit.
> - */
> -static int
> -xfs_writepage_map(
> -	struct xfs_writepage_ctx *wpc,
> -	struct writeback_control *wbc,
> -	struct inode		*inode,
> -	struct page		*page,
> -	uint64_t		end_offset)
> -{
> -	LIST_HEAD(submit_list);
> -	struct iomap_page	*iop = to_iomap_page(page);
> -	unsigned		len = i_blocksize(inode);
> -	struct xfs_ioend	*ioend, *next;
> -	uint64_t		file_offset;	/* file offset of page */
> -	int			error = 0, count = 0, i;
> -
> -	ASSERT(iop || i_blocksize(inode) == PAGE_SIZE);
> -	ASSERT(!iop || atomic_read(&iop->write_count) == 0);
> -
> -	/*
> -	 * Walk through the page to find areas to write back. If we run off the
> -	 * end of the current map or find the current map invalid, grab a new
> -	 * one.
> -	 */
> -	for (i = 0, file_offset = page_offset(page);
> -	     i < (PAGE_SIZE >> inode->i_blkbits) && file_offset < end_offset;
> -	     i++, file_offset += len) {
> -		if (iop && !test_bit(i, iop->uptodate))
> -			continue;
> -
> -		error = xfs_map_blocks(wpc, inode, file_offset);
> -		if (error)
> -			break;
> -		if (wpc->iomap.type == IOMAP_HOLE)
> -			continue;
> -		xfs_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
> -				 &submit_list);
> -		count++;
> -	}
> -
> -	ASSERT(wpc->ioend || list_empty(&submit_list));
> -	ASSERT(PageLocked(page));
> -	ASSERT(!PageWriteback(page));
> -
> -	/*
> -	 * On error, we have to fail the ioend here because we may have set
> -	 * pages under writeback, we have to make sure we run IO completion to
> -	 * mark the error state of the IO appropriately, so we can't cancel the
> -	 * ioend directly here.  That means we have to mark this page as under
> -	 * writeback if we included any blocks from it in the ioend chain so
> -	 * that completion treats it correctly.
> -	 *
> -	 * If we didn't include the page in the ioend, the on error we can
> -	 * simply discard and unlock it as there are no other users of the page
> -	 * now.  The caller will still need to trigger submission of outstanding
> -	 * ioends on the writepage context so they are treated correctly on
> -	 * error.
> -	 */
> -	if (unlikely(error)) {
> -		if (!count) {
> -			xfs_aops_discard_page(page);
> -			ClearPageUptodate(page);
> -			unlock_page(page);
> -			goto done;
> -		}
> -
> -		/*
> -		 * If the page was not fully cleaned, we need to ensure that the
> -		 * higher layers come back to it correctly.  That means we need
> -		 * to keep the page dirty, and for WB_SYNC_ALL writeback we need
> -		 * to ensure the PAGECACHE_TAG_TOWRITE index mark is not removed
> -		 * so another attempt to write this page in this writeback sweep
> -		 * will be made.
> -		 */
> -		set_page_writeback_keepwrite(page);
> -	} else {
> -		clear_page_dirty_for_io(page);
> -		set_page_writeback(page);
> -	}
> -
> -	unlock_page(page);
> -
> -	/*
> -	 * Preserve the original error if there was one, otherwise catch
> -	 * submission errors here and propagate into subsequent ioend
> -	 * submissions.
> -	 */
> -	list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
> -		int error2;
> -
> -		list_del_init(&ioend->io_list);
> -		error2 = xfs_submit_ioend(wbc, ioend, error);
> -		if (error2 && !error)
> -			error = error2;
> -	}
> -
> -	/*
> -	 * We can end up here with no error and nothing to write only if we race
> -	 * with a partial page truncate on a sub-page block sized filesystem.
> -	 */
> -	if (!count)
> -		end_page_writeback(page);
> -done:
> -	mapping_set_error(page->mapping, error);
> -	return error;
> -}
> -
> -/*
> - * Write out a dirty page.
> - *
> - * For delalloc space on the page we need to allocate space and flush it.
> - * For unwritten space on the page we need to start the conversion to
> - * regular allocated space.
> - */
> -STATIC int
> -xfs_do_writepage(
> -	struct page		*page,
> -	struct writeback_control *wbc,
> -	void			*data)
> -{
> -	struct xfs_writepage_ctx *wpc = data;
> -	struct inode		*inode = page->mapping->host;
> -	loff_t			offset;
> -	uint64_t              end_offset;
> -	pgoff_t                 end_index;
> -
> -	trace_xfs_writepage(inode, page, 0, 0);
> -
> -	/*
> -	 * Refuse to write the page out if we are called from reclaim context.
> -	 *
> -	 * This avoids stack overflows when called from deeply used stacks in
> -	 * random callers for direct reclaim or memcg reclaim.  We explicitly
> -	 * allow reclaim from kswapd as the stack usage there is relatively low.
> -	 *
> -	 * This should never happen except in the case of a VM regression so
> -	 * warn about it.
> -	 */
> -	if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> -			PF_MEMALLOC))
> -		goto redirty;
> -
> -	/*
> -	 * Given that we do not allow direct reclaim to call us, we should
> -	 * never be called while in a filesystem transaction.
> -	 */
> -	if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> -		goto redirty;
> -
> -	/*
> -	 * Is this page beyond the end of the file?
> -	 *
> -	 * The page index is less than the end_index, adjust the end_offset
> -	 * to the highest offset that this page should represent.
> -	 * -----------------------------------------------------
> -	 * |			file mapping	       | <EOF> |
> -	 * -----------------------------------------------------
> -	 * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
> -	 * ^--------------------------------^----------|--------
> -	 * |     desired writeback range    |      see else    |
> -	 * ---------------------------------^------------------|
> -	 */
> -	offset = i_size_read(inode);
> -	end_index = offset >> PAGE_SHIFT;
> -	if (page->index < end_index)
> -		end_offset = (xfs_off_t)(page->index + 1) << PAGE_SHIFT;
> -	else {
> -		/*
> -		 * Check whether the page to write out is beyond or straddles
> -		 * i_size or not.
> -		 * -------------------------------------------------------
> -		 * |		file mapping		        | <EOF>  |
> -		 * -------------------------------------------------------
> -		 * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
> -		 * ^--------------------------------^-----------|---------
> -		 * |				    |      Straddles     |
> -		 * ---------------------------------^-----------|--------|
> -		 */
> -		unsigned offset_into_page = offset & (PAGE_SIZE - 1);
> -
> -		/*
> -		 * Skip the page if it is fully outside i_size, e.g. due to a
> -		 * truncate operation that is in progress. We must redirty the
> -		 * page so that reclaim stops reclaiming it. Otherwise
> -		 * xfs_vm_releasepage() is called on it and gets confused.
> -		 *
> -		 * Note that the end_index is unsigned long, it would overflow
> -		 * if the given offset is greater than 16TB on 32-bit system
> -		 * and if we do check the page is fully outside i_size or not
> -		 * via "if (page->index >= end_index + 1)" as "end_index + 1"
> -		 * will be evaluated to 0.  Hence this page will be redirtied
> -		 * and be written out repeatedly which would result in an
> -		 * infinite loop, the user program that perform this operation
> -		 * will hang.  Instead, we can verify this situation by checking
> -		 * if the page to write is totally beyond the i_size or if it's
> -		 * offset is just equal to the EOF.
> -		 */
> -		if (page->index > end_index ||
> -		    (page->index == end_index && offset_into_page == 0))
> -			goto redirty;
> -
> -		/*
> -		 * The page straddles i_size.  It must be zeroed out on each
> -		 * and every writepage invocation because it may be mmapped.
> -		 * "A file is mapped in multiples of the page size.  For a file
> -		 * that is not a multiple of the page size, the remaining
> -		 * memory is zeroed when mapped, and writes to that region are
> -		 * not written out to the file."
> -		 */
> -		zero_user_segment(page, offset_into_page, PAGE_SIZE);
> -
> -		/* Adjust the end_offset to the end of file */
> -		end_offset = offset;
> -	}
> -
> -	return xfs_writepage_map(wpc, wbc, inode, page, end_offset);
> -
> -redirty:
> -	redirty_page_for_writepage(wbc, page);
> -	unlock_page(page);
> -	return 0;
> -}
> +static const struct iomap_writeback_ops xfs_writeback_ops = {
> +	.map_blocks		= xfs_map_blocks,
> +	.submit_ioend		= xfs_submit_ioend,
> +	.discard_page		= xfs_discard_page,
> +};
>  
>  STATIC int
>  xfs_vm_writepage(
> @@ -1114,12 +589,8 @@ xfs_vm_writepage(
>  	struct writeback_control *wbc)
>  {
>  	struct xfs_writepage_ctx wpc = { };
> -	int			ret;
>  
> -	ret = xfs_do_writepage(page, wbc, &wpc);
> -	if (wpc.ioend)
> -		ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
> -	return ret;
> +	return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);
>  }
>  
>  STATIC int
> @@ -1128,13 +599,9 @@ xfs_vm_writepages(
>  	struct writeback_control *wbc)
>  {
>  	struct xfs_writepage_ctx wpc = { };
> -	int			ret;
>  
>  	xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
> -	ret = write_cache_pages(mapping, wbc, xfs_do_writepage, &wpc);
> -	if (wpc.ioend)
> -		ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
> -	return ret;
> +	return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops);
>  }
>  
>  STATIC int
> @@ -1147,15 +614,6 @@ xfs_dax_writepages(
>  			xfs_find_bdev_for_inode(mapping->host), wbc);
>  }
>  
> -STATIC int
> -xfs_vm_releasepage(
> -	struct page		*page,
> -	gfp_t			gfp_mask)
> -{
> -	trace_xfs_releasepage(page->mapping->host, page, 0, 0);
> -	return iomap_releasepage(page, gfp_mask);
> -}
> -
>  STATIC sector_t
>  xfs_vm_bmap(
>  	struct address_space	*mapping,
> @@ -1213,8 +671,8 @@ const struct address_space_operations xfs_address_space_operations = {
>  	.writepage		= xfs_vm_writepage,
>  	.writepages		= xfs_vm_writepages,
>  	.set_page_dirty		= iomap_set_page_dirty,
> -	.releasepage		= xfs_vm_releasepage,
> -	.invalidatepage		= xfs_vm_invalidatepage,
> +	.releasepage		= iomap_releasepage,
> +	.invalidatepage		= iomap_invalidatepage,
>  	.bmap			= xfs_vm_bmap,
>  	.direct_IO		= noop_direct_IO,
>  	.migratepage		= iomap_migrate_page,
> diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
> index 4a0226cdad4f..687b11f34fa2 100644
> --- a/fs/xfs/xfs_aops.h
> +++ b/fs/xfs/xfs_aops.h
> @@ -6,23 +6,6 @@
>  #ifndef __XFS_AOPS_H__
>  #define __XFS_AOPS_H__
>  
> -extern struct bio_set xfs_ioend_bioset;
> -
> -/*
> - * Structure for buffered I/O completions.
> - */
> -struct xfs_ioend {
> -	struct list_head	io_list;	/* next ioend in chain */
> -	u16			io_type;
> -	u16			io_flags;	/* IOMAP_F_* */
> -	struct inode		*io_inode;	/* file being written to */
> -	size_t			io_size;	/* size of the extent */
> -	xfs_off_t		io_offset;	/* offset in the file */
> -	void			*io_private;	/* file system private data */
> -	struct bio		*io_bio;	/* bio being built */
> -	struct bio		io_inline_bio;	/* MUST BE LAST! */
> -};
> -
>  extern const struct address_space_operations xfs_address_space_operations;
>  extern const struct address_space_operations xfs_dax_aops;
>  
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 8d1df9f8be07..0a8cf6b87a21 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -40,7 +40,6 @@
>  #include <linux/parser.h>
>  
>  static const struct super_operations xfs_super_operations;
> -struct bio_set xfs_ioend_bioset;
>  
>  static struct kset *xfs_kset;		/* top-level xfs sysfs dir */
>  #ifdef DEBUG
> @@ -1853,15 +1852,10 @@ MODULE_ALIAS_FS("xfs");
>  STATIC int __init
>  xfs_init_zones(void)
>  {
> -	if (bioset_init(&xfs_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> -			offsetof(struct xfs_ioend, io_inline_bio),
> -			BIOSET_NEED_BVECS))
> -		goto out;
> -
>  	xfs_log_ticket_zone = kmem_zone_init(sizeof(xlog_ticket_t),
>  						"xfs_log_ticket");
>  	if (!xfs_log_ticket_zone)
> -		goto out_free_ioend_bioset;
> +		goto out;
>  
>  	xfs_bmap_free_item_zone = kmem_zone_init(
>  			sizeof(struct xfs_extent_free_item),
> @@ -1996,8 +1990,6 @@ xfs_init_zones(void)
>  	kmem_zone_destroy(xfs_bmap_free_item_zone);
>   out_destroy_log_ticket_zone:
>  	kmem_zone_destroy(xfs_log_ticket_zone);
> - out_free_ioend_bioset:
> -	bioset_exit(&xfs_ioend_bioset);
>   out:
>  	return -ENOMEM;
>  }
> @@ -2028,7 +2020,6 @@ xfs_destroy_zones(void)
>  	kmem_zone_destroy(xfs_btree_cur_zone);
>  	kmem_zone_destroy(xfs_bmap_free_item_zone);
>  	kmem_zone_destroy(xfs_log_ticket_zone);
> -	bioset_exit(&xfs_ioend_bioset);
>  }
>  
>  STATIC int __init
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index eae4b29c174e..cbb23d7a3554 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -1158,45 +1158,6 @@ DEFINE_RW_EVENT(xfs_file_buffered_write);
>  DEFINE_RW_EVENT(xfs_file_direct_write);
>  DEFINE_RW_EVENT(xfs_file_dax_write);
>  
> -DECLARE_EVENT_CLASS(xfs_page_class,
> -	TP_PROTO(struct inode *inode, struct page *page, unsigned long off,
> -		 unsigned int len),
> -	TP_ARGS(inode, page, off, len),
> -	TP_STRUCT__entry(
> -		__field(dev_t, dev)
> -		__field(xfs_ino_t, ino)
> -		__field(pgoff_t, pgoff)
> -		__field(loff_t, size)
> -		__field(unsigned long, offset)
> -		__field(unsigned int, length)
> -	),
> -	TP_fast_assign(
> -		__entry->dev = inode->i_sb->s_dev;
> -		__entry->ino = XFS_I(inode)->i_ino;
> -		__entry->pgoff = page_offset(page);
> -		__entry->size = i_size_read(inode);
> -		__entry->offset = off;
> -		__entry->length = len;
> -	),
> -	TP_printk("dev %d:%d ino 0x%llx pgoff 0x%lx size 0x%llx offset %lx "
> -		  "length %x",
> -		  MAJOR(__entry->dev), MINOR(__entry->dev),
> -		  __entry->ino,
> -		  __entry->pgoff,
> -		  __entry->size,
> -		  __entry->offset,
> -		  __entry->length)
> -)
> -
> -#define DEFINE_PAGE_EVENT(name)		\
> -DEFINE_EVENT(xfs_page_class, name,	\
> -	TP_PROTO(struct inode *inode, struct page *page, unsigned long off, \
> -		 unsigned int len),	\
> -	TP_ARGS(inode, page, off, len))
> -DEFINE_PAGE_EVENT(xfs_writepage);
> -DEFINE_PAGE_EVENT(xfs_releasepage);
> -DEFINE_PAGE_EVENT(xfs_invalidatepage);
> -
>  DECLARE_EVENT_CLASS(xfs_imap_class,
>  	TP_PROTO(struct xfs_inode *ip, xfs_off_t offset, ssize_t count,
>  		 int whichfork, struct xfs_bmbt_irec *irec),
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 7aa5d6117936..0b399718c387 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -4,6 +4,7 @@
>  
>  #include <linux/atomic.h>
>  #include <linux/bitmap.h>
> +#include <linux/blk_types.h>
>  #include <linux/mm.h>
>  #include <linux/types.h>
>  #include <linux/mm_types.h>
> @@ -12,6 +13,7 @@
>  struct address_space;
>  struct fiemap_extent_info;
>  struct inode;
> +struct iomap_writepage_ctx;
>  struct iov_iter;
>  struct kiocb;
>  struct page;
> @@ -183,6 +185,63 @@ loff_t iomap_seek_data(struct inode *inode, loff_t offset,
>  sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
>  		const struct iomap_ops *ops);
>  
> +/*
> + * Structure for writeback I/O completions.
> + */
> +struct iomap_ioend {
> +	struct list_head	io_list;	/* next ioend in chain */
> +	u16			io_type;
> +	u16			io_flags;	/* IOMAP_F_* */
> +	struct inode		*io_inode;	/* file being written to */
> +	size_t			io_size;	/* size of the extent */
> +	loff_t			io_offset;	/* offset in the file */
> +	void			*io_private;	/* file system private data */
> +	struct bio		*io_bio;	/* bio being built */
> +	struct bio		io_inline_bio;	/* MUST BE LAST! */
> +};
> +
> +struct iomap_writeback_ops {
> +	/*
> +	 * Required, maps the blocks so that writeback can be performed on
> +	 * the range starting at offset.
> +	 */
> +	int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode,
> +				loff_t offset);
> +
> +	/*
> +	 * Optional, allows the file systems to perform actions just before
> +	 * submitting the bio and/or override the bio end_io handler for complex
> +	 * operations like copy on write extent manipulation or unwritten extent
> +	 * conversions.
> +	 */
> +	int (*submit_ioend)(struct iomap_ioend *ioend, int status);
> +
> +	/*
> +	 * Optional, allows the file system to discard state on a page where
> +	 * we failed to submit any I/O.
> +	 */
> +	void (*discard_page)(struct page *page);
> +};
> +
> +struct iomap_writepage_ctx {
> +	struct iomap		iomap;
> +	struct iomap_ioend	*ioend;
> +	const struct iomap_writeback_ops *ops;
> +};
> +
> +void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
> +void iomap_ioend_try_merge(struct iomap_ioend *ioend,
> +		struct list_head *more_ioends,
> +		void (*merge_private)(struct iomap_ioend *ioend,
> +				struct iomap_ioend *next));
> +void iomap_sort_ioends(struct list_head *ioend_list);
> +int iomap_writepage(struct page *page, struct writeback_control *wbc,
> +		struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops);
> +int iomap_writepages(struct address_space *mapping,
> +		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops);
> +
>  /*
>   * Flags for direct I/O ->end_io:
>   */
> -- 
> 2.20.1
>