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    SubjectRe: [PATCH v3] iomap: support tail packing inline read
    Am Mo., 19. Juli 2021 um 16:48 Uhr schrieb Gao Xiang
    <hsiangkao@linux.alibaba.com>:
    > This tries to add tail packing inline read to iomap, which can support
    > several inline tail blocks. Similar to the previous approach, it cleans
    > post-EOF in one iteration.
    >
    > The write path remains untouched since EROFS cannot be used for testing.
    > It'd be better to be implemented if upcoming real users care rather than
    > leave untested dead code around.
    >
    > Cc: Christoph Hellwig <hch@lst.de>
    > Cc: Darrick J. Wong <djwong@kernel.org>
    > Cc: Matthew Wilcox <willy@infradead.org>
    > Cc: Andreas Gruenbacher <andreas.gruenbacher@gmail.com>
    > Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
    > ---
    > v2: https://lore.kernel.org/r/YPLdSja%2F4FBsjss%2F@B-P7TQMD6M-0146.local/
    > changes since v2:
    > - update suggestion from Christoph:
    > https://lore.kernel.org/r/YPVe41YqpfGLNsBS@infradead.org/
    >
    > Hi Andreas,
    > would you mind test on the gfs2 side? Thanks in advance!
    >
    > Thanks,
    > Gao Xiang
    >
    > fs/iomap/buffered-io.c | 50 ++++++++++++++++++++++++++----------------
    > fs/iomap/direct-io.c | 11 ++++++----
    > 2 files changed, 38 insertions(+), 23 deletions(-)
    >
    > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
    > index 87ccb3438bec..cac8a88660d8 100644
    > --- a/fs/iomap/buffered-io.c
    > +++ b/fs/iomap/buffered-io.c
    > @@ -207,23 +207,22 @@ struct iomap_readpage_ctx {
    >
    > static void
    > iomap_read_inline_data(struct inode *inode, struct page *page,
    > - struct iomap *iomap)
    > + struct iomap *iomap, loff_t pos)
    > {
    > - size_t size = i_size_read(inode);
    > + unsigned int size, poff = offset_in_page(pos);
    > void *addr;
    >
    > - if (PageUptodate(page))
    > - return;
    > -
    > - BUG_ON(page_has_private(page));
    > - BUG_ON(page->index);
    > - BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
    > + /* inline source data must be inside a single page */
    > + BUG_ON(iomap->length > PAGE_SIZE - offset_in_page(iomap->inline_data));
    > + /* handle tail-packing blocks cross the current page into the next */
    > + size = min_t(unsigned int, iomap->length + pos - iomap->offset,
    > + PAGE_SIZE - poff);

    Hmm, so EROFS really does multi-page tail packing? This contradicts
    the comment and code in iomap_dio_inline_actor.

    > addr = kmap_atomic(page);
    > - memcpy(addr, iomap->inline_data, size);
    > - memset(addr + size, 0, PAGE_SIZE - size);
    > + memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size);
    > + memset(addr + poff + size, 0, PAGE_SIZE - poff - size);
    > kunmap_atomic(addr);
    > - SetPageUptodate(page);
    > + iomap_set_range_uptodate(page, poff, PAGE_SIZE - poff);
    > }

    It's been said before, but iomap_read_inline_data should return
    PAGE_SIZE - poff, and no (void) casting when the return value is
    ignored.

    > static inline bool iomap_block_needs_zeroing(struct inode *inode,
    > @@ -246,18 +245,19 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
    > unsigned poff, plen;
    > sector_t sector;
    >
    > - if (iomap->type == IOMAP_INLINE) {
    > - WARN_ON_ONCE(pos);
    > - iomap_read_inline_data(inode, page, iomap);
    > - return PAGE_SIZE;
    > - }
    > -
    > - /* zero post-eof blocks as the page may be mapped */
    > iop = iomap_page_create(inode, page);
    > + /* needs to skip some leading uptodated blocks */

    "needs to skip some leading uptodate blocks"

    > iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
    > if (plen == 0)
    > goto done;
    >
    > + if (iomap->type == IOMAP_INLINE) {
    > + iomap_read_inline_data(inode, page, iomap, pos);
    > + plen = PAGE_SIZE - poff;
    > + goto done;
    > + }
    > +
    > + /* zero post-eof blocks as the page may be mapped */
    > if (iomap_block_needs_zeroing(inode, iomap, pos)) {
    > zero_user(page, poff, plen);
    > iomap_set_range_uptodate(page, poff, plen);
    > @@ -589,6 +589,18 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
    > return 0;
    > }
    >
    > +static int iomap_write_begin_inline(struct inode *inode, loff_t pos,
    > + struct page *page, struct iomap *srcmap)
    > +{
    > + /* needs more work for the tailpacking case, disable for now */
    > + if (WARN_ON_ONCE(pos != 0))

    This should be a WARN_ON_ONCE(srcmap->offset != 0). Otherwise, something like:

    xfs_io -ft -c 'pwrite 1 2'

    will fail because pos will be 1.

    > + return -EIO;
    > + if (PageUptodate(page))
    > + return 0;
    > + iomap_read_inline_data(inode, page, srcmap, pos);

    The above means that passing pos to iomap_read_inline_data here won't
    do the right thing, either.

    > + return 0;
    > +}
    > +
    > static int
    > iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
    > struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
    > @@ -618,7 +630,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
    > }
    >
    > if (srcmap->type == IOMAP_INLINE)
    > - iomap_read_inline_data(inode, page, srcmap);
    > + status = iomap_write_begin_inline(inode, pos, page, srcmap);
    > else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
    > status = __block_write_begin_int(page, pos, len, NULL, srcmap);
    > else
    > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
    > index 9398b8c31323..ee6309967b77 100644
    > --- a/fs/iomap/direct-io.c
    > +++ b/fs/iomap/direct-io.c
    > @@ -379,22 +379,25 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
    > {
    > struct iov_iter *iter = dio->submit.iter;
    > size_t copied;
    > + void *dst = iomap->inline_data + pos - iomap->offset;
    >
    > - BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
    > + /* inline data must be inside a single page */
    > + BUG_ON(length > PAGE_SIZE - offset_in_page(iomap->inline_data));
    >
    > if (dio->flags & IOMAP_DIO_WRITE) {
    > loff_t size = inode->i_size;
    >
    > if (pos > size)
    > - memset(iomap->inline_data + size, 0, pos - size);
    > - copied = copy_from_iter(iomap->inline_data + pos, length, iter);
    > + memset(iomap->inline_data + size - iomap->offset,
    > + 0, pos - size);
    > + copied = copy_from_iter(dst, length, iter);
    > if (copied) {
    > if (pos + copied > size)
    > i_size_write(inode, pos + copied);
    > mark_inode_dirty(inode);
    > }
    > } else {
    > - copied = copy_to_iter(iomap->inline_data + pos, length, iter);
    > + copied = copy_to_iter(dst, length, iter);
    > }
    > dio->size += copied;
    > return copied;
    > --
    > 2.24.4
    >

    Thanks,
    Andreas

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