On Mon, Nov 30, 2020 at 07:37:16PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> Add a copy_file_range handler to XFS so that we can accelerate file
> copies with reflink when the source and destination ranges are not
> block-aligned. We'll use the generic pagecache copy to handle the
> unaligned edges and attempt to reflink the middle.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> fs/xfs/xfs_file.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 99 insertions(+)
>
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 5b0f93f73837..9d1bb0dc30e2 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1119,6 +1119,104 @@ xfs_file_remap_range(
> return remapped > 0 ? remapped : ret;
> }
>
...
> +STATIC ssize_t
> +xfs_file_copy_range(
> + struct file *src_file,
> + loff_t src_off,
> + struct file *dst_file,
> + loff_t dst_off,
> + size_t len,
> + unsigned int flags)
> +{
> + struct inode *inode_src = file_inode(src_file);
> + struct xfs_inode *src = XFS_I(inode_src);
> + struct inode *inode_dst = file_inode(dst_file);
> + struct xfs_inode *dst = XFS_I(inode_dst);
> + struct xfs_mount *mp = src->i_mount;
> + loff_t copy_ret;
> + loff_t next_block;
> + size_t copy_len;
> + ssize_t total_copied = 0;
> +
> + /* Bypass all this if no copy acceleration is possible. */
> + if (!xfs_want_reflink_copy_range(src, src_off, dst, dst_off, len))
> + goto use_generic;
> +
> + /* Use the regular copy until we're block aligned at the start. */
> + next_block = round_up(src_off + 1, mp->m_sb.sb_blocksize);
Why the +1? AFAICT this means we manually copy the first block if
src_off does happen to be block aligned. Is this an assumption based on
the caller attempting ->remap_file_range() first?
BTW, if we do happen to be called in some (theoretical) corner case
where remap doesn't work unrelated to alignment, it seems this would
unconditionally break the manual copy into multiple parts (first block +
the rest). It's not immediately clear to me if that's significant from a
performance perspective, but I wonder if it would be nicer here to
filter that out more explicitly. For example, run the remap checks on
the block aligned offset/len first, or skip the remap if the caller has
provided a block aligned start (i.e. hinting that remap failed for other
reasons), or perhaps even implement this so it conditionally performs a
short manual copy so the next retry would fall into ->remap_file_range()
with aligned offsets, etc. Thoughts?
> + copy_len = min_t(size_t, len, next_block - src_off);
> + if (copy_len > 0) {
> + copy_ret = generic_copy_file_range(src_file, src_off, dst_file,
> + dst_off, copy_len, flags);
> + if (copy_ret < 0)
> + return copy_ret;
> +
> + src_off += copy_ret;
> + dst_off += copy_ret;
> + len -= copy_ret;
> + total_copied += copy_ret;
> + if (copy_ret < copy_len || len == 0)
> + return total_copied;
> + }
> +
> + /*
> + * Now try to reflink as many full blocks as we can. If the end of the
> + * copy request wasn't block-aligned or the reflink fails, we'll just
> + * fall into the generic copy to do the rest.
> + */
> + copy_len = round_down(len, mp->m_sb.sb_blocksize);
> + if (copy_len > 0) {
> + copy_ret = xfs_file_remap_range(src_file, src_off, dst_file,
> + dst_off, copy_len, REMAP_FILE_CAN_SHORTEN);
> + if (copy_ret >= 0) {
> + src_off += copy_ret;
> + dst_off += copy_ret;
> + len -= copy_ret;
> + total_copied += copy_ret;
> + if (copy_ret < copy_len || len == 0)
> + return total_copied;
Any reason we return a potential short copy here, but fall into the
manual copy if the reflink outright fails?
> + }
> + }
> +
> +use_generic:
> + /* Use the regular copy to deal with leftover bytes. */
> + copy_ret = generic_copy_file_range(src_file, src_off, dst_file,
> + dst_off, len, flags);
> + if (copy_ret < 0)
> + return copy_ret;
Perhaps this should also check/return total_copied in the event we've
already done some work..?
Brian
> + return total_copied + copy_ret;
> +}
> +
> STATIC int
> xfs_file_open(
> struct inode *inode,
> @@ -1381,6 +1479,7 @@ const struct file_operations xfs_file_operations = {
> .get_unmapped_area = thp_get_unmapped_area,
> .fallocate = xfs_file_fallocate,
> .fadvise = xfs_file_fadvise,
> + .copy_file_range = xfs_file_copy_range,
> .remap_file_range = xfs_file_remap_range,
> };
>
>
