Re: [PATCH v14 105/138] iomap: Convert iomap_add_to_ioend to take a folio

Darrick J. Wong
2021-07-15T22:01:26Z

On Thu, Jul 15, 2021 at 04:36:31AM +0100, Matthew Wilcox (Oracle) wrote:
> We still iterate one block at a time, but now we call compound_head()
> less often. Rename file_offset to pos to fit the rest of the file.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> fs/iomap/buffered-io.c | 66 +++++++++++++++++++-----------------------
> 1 file changed, 30 insertions(+), 36 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index ac33f19325ab..8e767aec8d07 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1252,36 +1252,29 @@ iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t offset,
> * 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,
> +iomap_add_to_ioend(struct inode *inode, loff_t pos, struct folio *folio,
> 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);
> + sector_t sector = iomap_sector(&wpc->iomap, pos);
> unsigned len = i_blocksize(inode);
> - unsigned poff = offset & (PAGE_SIZE - 1);
> - bool merged, same_page = false;
> + size_t poff = offset_in_folio(folio, pos);
>
> - if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, offset, sector)) {
> + if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos, sector)) {
> if (wpc->ioend)
> list_add(&wpc->ioend->io_list, iolist);
> - wpc->ioend = iomap_alloc_ioend(inode, wpc, offset, sector, wbc);
> + wpc->ioend = iomap_alloc_ioend(inode, wpc, pos, sector, wbc);
> }
>
> - merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
> - &same_page);
> if (iop)
> atomic_add(len, &iop->write_bytes_pending);
> -
> - 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);
> + if (!bio_add_folio(wpc->ioend->io_bio, folio, len, poff)) {
> + wpc->ioend->io_bio = iomap_chain_bio(wpc->ioend->io_bio);
> + bio_add_folio(wpc->ioend->io_bio, folio, len, poff);

The paranoiac in me wonders if we ought to have some sort of error
checking here just in case we encounter double failures?

> }
>
> wpc->ioend->io_size += len;
> - wbc_account_cgroup_owner(wbc, page, len);
> + wbc_account_cgroup_owner(wbc, &folio->page, len);
> }
>
> /*
> @@ -1309,40 +1302,41 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> struct iomap_page *iop = to_iomap_page(folio);
> struct iomap_ioend *ioend, *next;
> unsigned len = i_blocksize(inode);
> - u64 file_offset; /* file offset of page */
> + unsigned nblocks = i_blocks_per_folio(inode, folio);
> + loff_t pos = folio_pos(folio);
> int error = 0, count = 0, i;
> LIST_HEAD(submit_list);
>
> - WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
> + WARN_ON_ONCE(nblocks > 1 && !iop);
> WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 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.
> + * Walk through the folio 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) {
> + for (i = 0; i < nblocks; i++, pos += len) {
> + if (pos >= end_offset)
> + break;

Any particular reason this isn't:

for (i = 0; i < nblocks && pos < end_offset; i++, pos += len) {

?

Everything from here on out looks decent to me.

--D

> if (iop && !test_bit(i, iop->uptodate))
> continue;
>
> - error = wpc->ops->map_blocks(wpc, inode, file_offset);
> + error = wpc->ops->map_blocks(wpc, inode, pos);
> if (error)
> break;
> if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
> continue;
> if (wpc->iomap.type == IOMAP_HOLE)
> continue;
> - iomap_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
> + iomap_add_to_ioend(inode, pos, folio, 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));
> - WARN_ON_ONCE(PageDirty(page));
> + WARN_ON_ONCE(!folio_test_locked(folio));
> + WARN_ON_ONCE(folio_test_writeback(folio));
> + WARN_ON_ONCE(folio_test_dirty(folio));
>
> /*
> * We cannot cancel the ioend directly here on error. We may have
> @@ -1358,16 +1352,16 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> * now.
> */
> if (wpc->ops->discard_page)
> - wpc->ops->discard_page(page, file_offset);
> + wpc->ops->discard_page(&folio->page, pos);
> if (!count) {
> - ClearPageUptodate(page);
> - unlock_page(page);
> + folio_clear_uptodate(folio);
> + folio_unlock(folio);
> goto done;
> }
> }
>
> - set_page_writeback(page);
> - unlock_page(page);
> + folio_start_writeback(folio);
> + folio_unlock(folio);
>
> /*
> * Preserve the original error if there was one, otherwise catch
> @@ -1388,9 +1382,9 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> * with a partial page truncate on a sub-page block sized filesystem.
> */
> if (!count)
> - end_page_writeback(page);
> + folio_end_writeback(folio);
> done:
> - mapping_set_error(page->mapping, error);
> + mapping_set_error(folio->mapping, error);
> return error;
> }
>
> --
> 2.30.2
>