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SubjectRe: [PATCH 10/11] xfs: use the iomap write page code
On Tue, Oct 01, 2019 at 09:11:51AM +0200, Christoph Hellwig wrote:
> Use the new iomap writeback code that was copied from XFS to perform
> writeback.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> [darrick: reduce this patch only to convert the xfs writeback code]
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Just a few nit level comments..

> fs/xfs/xfs_aops.c | 667 +++++----------------------------------------
> fs/xfs/xfs_aops.h | 17 --
> fs/xfs/xfs_super.c | 11 +-
> fs/xfs/xfs_trace.h | 39 ---
> 4 files changed, 74 insertions(+), 660 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 8c101081e3b1..d0a25b822123 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
...
> @@ -397,22 +265,16 @@ 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 ((ioend->io_flags & IOMAP_F_SHARED) ||
> - ioend->io_type == IOMAP_UNWRITTEN ||
> - ioend->io_append_trans != NULL) {
> - 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));

This change is a bit subtle. I think it would be good to have a new
assert here to ensure that we only ever end up in this handler for
appropriate ioends (i.e., shared || unwritten || append).

> + 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);
> }
>
> /*
...
> @@ -630,24 +497,9 @@ xfs_map_blocks(
...
> +static int
> xfs_submit_ioend(
> - struct writeback_control *wbc,
> - struct xfs_ioend *ioend,
> + struct iomap_ioend *ioend,
> int status)
> {
> unsigned int nofs_flag;
> @@ -670,139 +522,15 @@ xfs_submit_ioend(
> ((ioend->io_flags & IOMAP_F_SHARED) ||
> ioend->io_type != IOMAP_UNWRITTEN) &&
> xfs_ioend_is_append(ioend) &&
> - !ioend->io_append_trans)
> + !ioend->io_private)
> status = xfs_setfilesize_trans_alloc(ioend);
>
> memalloc_nofs_restore(nofs_flag);
...
> + if ((ioend->io_flags & IOMAP_F_SHARED) ||
> + ioend->io_type == IOMAP_UNWRITTEN ||
> + ioend->io_private)
> + ioend->io_bio->bi_end_io = xfs_end_bio;
> + return status;

Somewhat related to the previous comment, but FWIW I find the
->submit_ioend() callback semantics a bit confusing in terms of what
layer is responsible for callback assignment, submitting/cancelling
bios, etc.

If we stick with the current semantics, could we add a function header
comment to document it clearly? IMO, something as simple as the
following is sufficient and helps set context:

/*
* Perform any pre-submit operations that might be necessary for the ioend.
* Replace the default iomap bio completion handler if custom completion time
* processing is required.
*/

Also, could we consider a less misleading callback name?
->pre_submit_ioend() for example?

Those nits aside the rest of the patch looks good to me.

Brian

> }
>
> /*
> @@ -816,8 +544,8 @@ 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;
> @@ -839,246 +567,14 @@ 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);
> -}
> -
> -/*
> - * 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;
> + iomap_invalidatepage(page, 0, PAGE_SIZE);
> }
>
> -/*
> - * 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(
> @@ -1086,12 +582,8 @@ 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
> @@ -1100,13 +592,9 @@ 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
> @@ -1119,15 +607,6 @@ 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,
> @@ -1185,8 +664,8 @@ 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 c2756ed50b0d..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 */
> - struct xfs_trans *io_append_trans;/* xact. for size update */
> - 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),
> --
> 2.20.1
>

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