Re: [PATCH 18/21] iomap: Convert iomap_add_to_ioend to take a folio

Darrick J. Wong
2021-11-03T16:00:59Z

On Tue, Nov 02, 2021 at 08:28:02PM +0000, Matthew Wilcox wrote:
> On Tue, Nov 02, 2021 at 12:26:42AM -0700, Christoph Hellwig wrote:
> > Looking at the code not part of the context this looks fine. But I
> > really wonder if this (and also the blocks change above) would be
> > better off being split into separate, clearly documented patches.
>
> How do these three patches look? I retained your R-b on all three since
> I figured the one you offered below was good for all of them.

(TLDR: I have two RVB and a question about the third patch, please
scroll down...)

> From ab7cace8f325ca5cc1b1e62e6a8498c84738bc10 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Tue, 2 Nov 2021 10:51:55 -0400
> Subject: [PATCH 1/3] iomap: Simplify iomap_writepage_map()
>
> Rename end_offset to end_pos and file_offset to pos to match the
> rest of the file. Simplify the loop by calculating nblocks
> up front instead of each time around the loop.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/iomap/buffered-io.c | 21 ++++++++++-----------
> 1 file changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 8f47879f9f05..e32e3cb2cf86 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1296,37 +1296,36 @@ iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
> static int
> iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> struct writeback_control *wbc, struct inode *inode,
> - struct page *page, u64 end_offset)
> + struct page *page, loff_t end_pos)
> {
> struct folio *folio = page_folio(page);
> struct iomap_page *iop = iomap_page_create(inode, 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(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 && pos < end_pos; i++, pos += len) {
> 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, page, iop, wpc, wbc,
> &submit_list);
> count++;
> }
> @@ -1350,7 +1349,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> * now.
> */
> if (wpc->ops->discard_folio)
> - wpc->ops->discard_folio(page_folio(page), file_offset);
> + wpc->ops->discard_folio(folio, pos);

/me wonders why this wouldn't have been done in whichever patch added
folio as a local variable, but fmeh, the end result is the same:

Pretty straightforward conversion,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

(onto the next patch)

> if (!count) {
> ClearPageUptodate(page);
> unlock_page(page);
> --
> 2.33.0
>
>
> From 07c994353e357c3b4252595a80b86e8565deb09c Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Tue, 2 Nov 2021 11:41:16 -0400
> Subject: [PATCH 2/3] iomap: Simplify iomap_do_writepage()
>
> Rename end_offset to end_pos and offset_into_page to poff to match the
> rest of the file. Simplify the handling of the last page straddling
> i_size.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/iomap/buffered-io.c | 23 ++++++++++-------------
> 1 file changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index e32e3cb2cf86..4f4f33849417 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1397,9 +1397,7 @@ 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;
> + loff_t end_pos, isize;
>
> trace_iomap_writepage(inode, page_offset(page), PAGE_SIZE);
>
> @@ -1430,11 +1428,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * | 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 {
> + isize = i_size_read(inode);
> + end_pos = page_offset(page) + PAGE_SIZE;
> + if (end_pos - 1 >= isize) {

This old code was good at twisting my brain in knots, thanks for
cleaning this up.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

(onto the third patch)

> /*
> * Check whether the page to write out is beyond or straddles
> * i_size or not.
> @@ -1446,7 +1442,8 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * | | Straddles |
> * ---------------------------------^-----------|--------|
> */
> - unsigned offset_into_page = offset & (PAGE_SIZE - 1);
> + size_t poff = offset_in_page(isize);
> + pgoff_t end_index = isize >> PAGE_SHIFT;
>
> /*
> * Skip the page if it's fully outside i_size, e.g. due to a
> @@ -1466,7 +1463,7 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * offset is just equal to the EOF.
> */
> if (page->index > end_index ||
> - (page->index == end_index && offset_into_page == 0))
> + (page->index == end_index && poff == 0))
> goto redirty;
>
> /*
> @@ -1477,13 +1474,13 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * 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);
> + zero_user_segment(page, poff, PAGE_SIZE);
>
> /* Adjust the end_offset to the end of file */
> - end_offset = offset;
> + end_pos = isize;
> }
>
> - return iomap_writepage_map(wpc, wbc, inode, page, end_offset);
> + return iomap_writepage_map(wpc, wbc, inode, page, end_pos);
>
> redirty:
> redirty_page_for_writepage(wbc, page);
> --
> 2.33.0
>
>
> From d5412657a503ae27efb5770fbc1c5c980180c9c4 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Tue, 2 Nov 2021 12:45:12 -0400
> Subject: [PATCH 3/3] iomap: Convert iomap_add_to_ioend to take a folio
>
> We still iterate one block at a time, but now we call compound_head()
> less often.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/iomap/buffered-io.c | 70 ++++++++++++++++++++----------------------
> 1 file changed, 34 insertions(+), 36 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 4f4f33849417..8908368abd49 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1252,29 +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);
> + 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);
> }
>
> - if (bio_add_page(wpc->ioend->io_bio, page, len, poff) != len) {
> + if (!bio_add_folio(wpc->ioend->io_bio, folio, len, poff)) {
> wpc->ioend->io_bio = iomap_chain_bio(wpc->ioend->io_bio);
> - __bio_add_page(wpc->ioend->io_bio, page, len, poff);
> + bio_add_folio(wpc->ioend->io_bio, folio, len, poff);
> }
>
> if (iop)
> atomic_add(len, &iop->write_bytes_pending);
> wpc->ioend->io_size += len;
> - wbc_account_cgroup_owner(wbc, page, len);
> + wbc_account_cgroup_owner(wbc, &folio->page, len);
> }
>
> /*
> @@ -1296,9 +1296,8 @@ iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
> static int
> iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> struct writeback_control *wbc, struct inode *inode,
> - struct page *page, loff_t end_pos)
> + struct folio *folio, loff_t end_pos)
> {
> - struct folio *folio = page_folio(page);
> struct iomap_page *iop = iomap_page_create(inode, folio);
> struct iomap_ioend *ioend, *next;
> unsigned len = i_blocksize(inode);
> @@ -1325,15 +1324,15 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> continue;
> if (wpc->iomap.type == IOMAP_HOLE)
> continue;
> - iomap_add_to_ioend(inode, pos, 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
> @@ -1351,14 +1350,14 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> if (wpc->ops->discard_folio)
> wpc->ops->discard_folio(folio, 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; catch
> @@ -1379,9 +1378,9 @@ 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;
> }
>
> @@ -1395,14 +1394,15 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> static int
> iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> {
> + struct folio *folio = page_folio(page);
> struct iomap_writepage_ctx *wpc = data;
> - struct inode *inode = page->mapping->host;
> + struct inode *inode = folio->mapping->host;
> loff_t end_pos, isize;
>
> - trace_iomap_writepage(inode, page_offset(page), PAGE_SIZE);
> + trace_iomap_writepage(inode, folio_pos(folio), folio_size(folio));
>
> /*
> - * Refuse to write the page out if we're called from reclaim context.
> + * Refuse to write the folio out if we're 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
> @@ -1416,10 +1416,10 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> goto redirty;
>
> /*
> - * Is this page beyond the end of the file?
> + * Is this folio 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.
> + * The folio index is less than the end_index, adjust the end_pos
> + * to the highest offset that this folio should represent.
> * -----------------------------------------------------
> * | file mapping | <EOF> |
> * -----------------------------------------------------
> @@ -1429,7 +1429,7 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * ---------------------------------^------------------|
> */
> isize = i_size_read(inode);
> - end_pos = page_offset(page) + PAGE_SIZE;
> + end_pos = folio_pos(folio) + folio_size(folio);
> if (end_pos - 1 >= isize) {
> /*
> * Check whether the page to write out is beyond or straddles
> @@ -1442,7 +1442,7 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * | | Straddles |
> * ---------------------------------^-----------|--------|
> */
> - size_t poff = offset_in_page(isize);
> + size_t poff = offset_in_folio(folio, isize);
> pgoff_t end_index = isize >> PAGE_SHIFT;
>
> /*
> @@ -1462,8 +1462,8 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * checking if the page is totally beyond i_size or if its
> * offset is just equal to the EOF.
> */
> - if (page->index > end_index ||
> - (page->index == end_index && poff == 0))
> + if (folio->index > end_index ||
> + (folio->index == end_index && poff == 0))
> goto redirty;
>
> /*
> @@ -1474,17 +1474,15 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * memory is zeroed when mapped, and writes to that region are
> * not written out to the file."
> */
> - zero_user_segment(page, poff, PAGE_SIZE);
> -
> - /* Adjust the end_offset to the end of file */
> + zero_user_segment(&folio->page, poff, folio_size(folio));

Question: is &folio->page != page here? I guess the idea is that we
have a (potentially multi-page) folio straddling i_size, and we need to
zero everything in the whole folio after i_size. But then why not pass
the whole folio?

--D

> end_pos = isize;
> }
>
> - return iomap_writepage_map(wpc, wbc, inode, page, end_pos);
> + return iomap_writepage_map(wpc, wbc, inode, folio, end_pos);
>
> redirty:
> - redirty_page_for_writepage(wbc, page);
> - unlock_page(page);
> + folio_redirty_for_writepage(wbc, folio);
> + folio_unlock(folio);
> return 0;
> }
>
> --
> 2.33.0
>