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    SubjectRe: [PATCH v2 20/28] iomap: Convert iomap_write_begin() and iomap_write_end() to folios
    On Mon, Nov 08, 2021 at 04:05:43AM +0000, Matthew Wilcox (Oracle) wrote:
    > These functions still only work in PAGE_SIZE chunks, but there are
    > fewer conversions from tail to head pages as a result of this patch.
    >
    > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    > Reviewed-by: Christoph Hellwig <hch@lst.de>
    > ---
    > fs/iomap/buffered-io.c | 66 ++++++++++++++++++++----------------------
    > 1 file changed, 31 insertions(+), 35 deletions(-)
    >
    > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
    > index 9c61d12028ca..f4ae200adc4c 100644
    > --- a/fs/iomap/buffered-io.c
    > +++ b/fs/iomap/buffered-io.c

    <snip>

    > @@ -741,6 +737,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
    > long status = 0;
    >
    > do {
    > + struct folio *folio;
    > struct page *page;
    > unsigned long offset; /* Offset into pagecache page */
    > unsigned long bytes; /* Bytes to write to page */
    > @@ -764,16 +761,17 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
    > break;
    > }
    >
    > - status = iomap_write_begin(iter, pos, bytes, &page);
    > + status = iomap_write_begin(iter, pos, bytes, &folio);
    > if (unlikely(status))
    > break;
    >
    > + page = folio_file_page(folio, pos >> PAGE_SHIFT);
    > if (mapping_writably_mapped(iter->inode->i_mapping))
    > flush_dcache_page(page);
    >
    > copied = copy_page_from_iter_atomic(page, offset, bytes, i);

    Hrmm. In principle (or I guess even a subsequent patch), if we had
    multi-page folios, could we simply loop the pages in the folio instead
    of doing a single page and then calling back into iomap_write_begin to
    get (probably) the same folio?

    This looks like a fairly straightforward conversion, but I was wondering
    about that one little point...

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

    --D

    >
    > - status = iomap_write_end(iter, pos, bytes, copied, page);
    > + status = iomap_write_end(iter, pos, bytes, copied, folio);
    >
    > if (unlikely(copied != status))
    > iov_iter_revert(i, copied - status);
    > @@ -839,13 +837,13 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
    > do {
    > unsigned long offset = offset_in_page(pos);
    > unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length);
    > - struct page *page;
    > + struct folio *folio;
    >
    > - status = iomap_write_begin(iter, pos, bytes, &page);
    > + status = iomap_write_begin(iter, pos, bytes, &folio);
    > if (unlikely(status))
    > return status;
    >
    > - status = iomap_write_end(iter, pos, bytes, bytes, page);
    > + status = iomap_write_end(iter, pos, bytes, bytes, folio);
    > if (WARN_ON_ONCE(status == 0))
    > return -EIO;
    >
    > @@ -882,21 +880,19 @@ EXPORT_SYMBOL_GPL(iomap_file_unshare);
    > static s64 __iomap_zero_iter(struct iomap_iter *iter, loff_t pos, u64 length)
    > {
    > struct folio *folio;
    > - struct page *page;
    > int status;
    > size_t offset, bytes;
    >
    > - status = iomap_write_begin(iter, pos, length, &page);
    > + status = iomap_write_begin(iter, pos, length, &folio);
    > if (status)
    > return status;
    > - folio = page_folio(page);
    >
    > offset = offset_in_folio(folio, pos);
    > bytes = min_t(u64, folio_size(folio) - offset, length);
    > folio_zero_range(folio, offset, bytes);
    > folio_mark_accessed(folio);
    >
    > - return iomap_write_end(iter, pos, bytes, bytes, page);
    > + return iomap_write_end(iter, pos, bytes, bytes, folio);
    > }
    >
    > static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
    > --
    > 2.33.0
    >

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