On Fri, Jun 15, 2018 at 03:01:56PM +0200, Christoph Hellwig wrote:
> We can handle the existing cow mapping case as a special case directly
> in xfs_writepage_map, and share code for allocating delalloc blocks
> with regular I/O in xfs_map_blocks. This means we need to always
> call xfs_map_blocks for reflink inodes, but we can still skip most of
> the work if it turns out that there is no COW mapping overlapping the
> current block.
>
> As a subtle detail we need to start caching holes in the wpc to deal
> with the case of COW reservations between EOF. But we'll need that
> infrastructure later anyway, so this is no big deal.
>
> Based on a patch from Dave Chinner.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/xfs/xfs_aops.c | 186 ++++++++++++++++++++++------------------------
> fs/xfs/xfs_aops.h | 4 +-
> 2 files changed, 92 insertions(+), 98 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index c8fc6786b06c..ff27bdcc49a1 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
...
> @@ -887,22 +877,24 @@ xfs_writepage_map(
> if (wpc->imap_valid)
> wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
> offset);
> - if (!wpc->imap_valid) {
> - error = xfs_map_blocks(inode, offset, &wpc->imap,
> - wpc->io_type);
A comment would be nice here just so the purpose of the logic is clear
at a glance. E.g:
/*
* COW fork blocks can overlap data fork blocks even if the
* blocks aren't shared. COW I/O always takes precedent, so we
* must always check for overlap on reflink inodes unless the
* mapping is already COW.
*/
With something like that, this now looks pretty good to me:
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Note: I see that this code ends up shifted into xfs_map_blocks(). If
it's easier to add the comment in whatever patch touches that last,
that's fine too.
Brian
> + if (!wpc->imap_valid ||
> + (xfs_is_reflink_inode(XFS_I(inode)) &&
> + wpc->io_type != XFS_IO_COW)) {
> + error = xfs_map_blocks(wpc, inode, offset);
> if (error)
> goto out;
> wpc->imap_valid = xfs_imap_valid(inode, &wpc->imap,
> offset);
> }
> - if (wpc->imap_valid) {
> - lock_buffer(bh);
> - if (wpc->io_type != XFS_IO_OVERWRITE)
> - xfs_map_at_offset(inode, bh, &wpc->imap, offset);
> - xfs_add_to_ioend(inode, bh, offset, wpc, wbc, &submit_list);
> - count++;
> - }
>
> + if (!wpc->imap_valid || wpc->io_type == XFS_IO_HOLE)
> + continue;
> +
> + lock_buffer(bh);
> + if (wpc->io_type != XFS_IO_OVERWRITE)
> + xfs_map_at_offset(inode, bh, &wpc->imap, offset);
> + xfs_add_to_ioend(inode, bh, offset, wpc, wbc, &submit_list);
> + count++;
> } while (offset += len, ((bh = bh->b_this_page) != head));
>
> ASSERT(wpc->ioend || list_empty(&submit_list));
> diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
> index 694c85b03813..466d22e5bc36 100644
> --- a/fs/xfs/xfs_aops.h
> +++ b/fs/xfs/xfs_aops.h
> @@ -29,6 +29,7 @@ enum {
> XFS_IO_UNWRITTEN, /* covers allocated but uninitialized data */
> XFS_IO_OVERWRITE, /* covers already allocated extent */
> XFS_IO_COW, /* covers copy-on-write extent */
> + XFS_IO_HOLE, /* covers region without any block allocation */
> };
>
> #define XFS_IO_TYPES \
> @@ -36,7 +37,8 @@ enum {
> { XFS_IO_DELALLOC, "delalloc" }, \
> { XFS_IO_UNWRITTEN, "unwritten" }, \
> { XFS_IO_OVERWRITE, "overwrite" }, \
> - { XFS_IO_COW, "CoW" }
> + { XFS_IO_COW, "CoW" }, \
> + { XFS_IO_HOLE, "hole" }
>
> /*
> * Structure for buffered I/O completions.
> --
> 2.17.1
>
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