When copying up within the same fs, try to use f_op->clone_file_range().
This becomes very efficient when lower and upper are on the same fs
with file reflink support.
Tested correct behavior when lower and upper are on:
1. same ext4 (copy)
2. same xfs + reflink patches + mkfs.xfs (copy)
3. same xfs + reflink patches + mkfs.xfs -m reflink=1 (clone)
4. different xfs + reflink patches + mkfs.xfs -m reflink=1 (copy)
Verified that all the overlay xfstests pass in the 'same fs'
setups.
For comparison, on my laptop, xfstest overlay/001 (copy up of large
sparse files) takes less than 1 second in the xfs reflink setup vs.
25 seconds on the rest of the setups.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
Notes:
V1:
- Replace iteravite call to copy_file_range() with
a single atomic call to clone_file_range()
- Add a TODO comment to consider calling vfs_copy_file_range()
instead of do_splice_direct() (*)
(*) Changes suggested by Dave Chinner:
1. Move the cross-fs check from vfs_copy_file_range()
helper up to the copy_file_range syscall
2. Allow vfs_copy_file_range() to handle cross-fs copy
by falling back directly to do_splice_direct(),
without attempting copy_file_range()
3. Replace copy_up call to do_splice_direct()
with call to vfs_copy_file_range()
The benefits of these extra changes to real world use case
have not been demonstrated. In theory, these changes should benefit
a setup of lower and upper dirs both on the same nfs/cifs mount.
fs/overlayfs/copy_up.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 43fdc27..a3fd658 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -136,6 +136,21 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
goto out_fput;
}
+ /*
+ * When copying up within the same fs, try to use clone_file_range
+ */
+ if (file_inode(old_file)->i_sb == file_inode(new_file)->i_sb &&
+ new_file->f_op->clone_file_range) {
+ error = new_file->f_op->clone_file_range(old_file, 0,
+ new_file, 0,
+ len);
+ /* on failure to clone entire len, fallback to splice loop */
+ if (error)
+ error = 0;
+ else
+ len = 0;
+ }
+
/* FIXME: copy up sparse files efficiently */
while (len) {
size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
@@ -149,6 +164,7 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
break;
}
+ /* TODO: consider calling vfs_copy_file_range() instead */
bytes = do_splice_direct(old_file, &old_pos,
new_file, &new_pos,
this_len, SPLICE_F_MOVE);
--
2.7.4
--
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