On Tue, Dec 01, 2020 at 10:25:48AM -0500, Brian Foster wrote:
> 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?
Yes. The VFS always tries that 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,
I doubt it, since that's usually just copying around the pagecache.
> 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),
Yes, checking the block alignment is a good suggestion. Will fix.
> 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.
Hm. That could be a thing too, though my opinion is that we should make
as much progress as we can before exiting the kernel.
--D
> 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,
> > };
> >
> >
>
