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    SubjectRe: [PATCH v3] iomap: support tail packing inline read
    On Tue, Jul 20, 2021 at 01:34:58PM +0200, Andreas Grünbacher wrote:
    > 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);
    > >
    > > 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);
    > > }
    > >
    > > 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);
    >
    > We can skip creating the iop when reading the entire page.

    As I said before, I think it can be in a separated patch like
    https://lore.kernel.org/r/YPMkKfegS+9KzEhK@casper.infradead.org/
    and Christoph said it should be careful:
    https://lore.kernel.org/r/YPVfxn6%2FoCPBZpKu@infradead.org/

    Thanks,
    Gao Xiang

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