copy_file_range and user space tools to do copy fastest

[Steve French via samba-technical]

Are there any user space tools (other than our test tools and xfs_io
etc.) that support copy_file_range? Looks like at least cp and rsync
and dd don't. That syscall which now has been around a couple years,
and was reminded about at the LSF/MM summit a few days ago, presumably
is the 'best' way to copy a file fast since it tries all the
mechanisms (reflink etc.) in order.

Since copy_file_range syscall can be 100x or more faster for network
file systems than the alternative, was surprised when I noticed that
cp and rsync didn't support it. It doesn't look like rsync even
supports reflink either(although presumably if you call
copy_file_range you don't have to worry about that), and reads/writes
are 8K. See copy_file() in rsync/util.c

In the cp command it looks like it can call the FICLONE IOCTL (see
clone_file() in coreutils/src/copy.c) but doesn't call the expected
"copy_file_range" syscall.

In the dd command it doesn't call either - see dd_copy in corutils/src/dd.c

Since it can be 100x or more faster in some cases to call
copy_file_range than do reads/writes back and forth to do a copy
(especially if network or clustered backend or cloud), what tools are
the best to recommend?

Would rsync or cp be likely to take patches to call the standard
"copy_file_range" syscall
(http://man7.org/linux/man-pages/man2/copy_file_range.2.html)?
Presumably not if it has been two+ years ... but would be interested
what copy tools to recommend to use instead.

These are not uncommon cases (all Windows, Macs, Samba etc. and even
some NFS servers) ... but copies over local file systems can benefit
too (as copy_file_range tries various mechanisms).

[Andreas Dilger via samba-technical]

Post by Steve French via samba-technical
Are there any user space tools (other than our test tools and xfs_io
etc.) that support copy_file_range? Looks like at least cp and rsync
and dd don't. That syscall which now has been around a couple years,
and was reminded about at the LSF/MM summit a few days ago, presumably
is the 'best' way to copy a file fast since it tries all the
mechanisms (reflink etc.) in order.
Since copy_file_range syscall can be 100x or more faster for network
file systems than the alternative, was surprised when I noticed that
cp and rsync didn't support it. It doesn't look like rsync even
supports reflink either(although presumably if you call
copy_file_range you don't have to worry about that), and reads/writes
are 8K. See copy_file() in rsync/util.c
In the cp command it looks like it can call the FICLONE IOCTL (see
clone_file() in coreutils/src/copy.c) but doesn't call the expected
"copy_file_range" syscall.
In the dd command it doesn't call either - see dd_copy in corutils/src/dd.c
Since it can be 100x or more faster in some cases to call
copy_file_range than do reads/writes back and forth to do a copy
(especially if network or clustered backend or cloud), what tools are
the best to recommend?
Would rsync or cp be likely to take patches to call the standard
"copy_file_range" syscall
(http://man7.org/linux/man-pages/man2/copy_file_range.2.html)?
Presumably not if it has been two+ years ... but would be interested
what copy tools to recommend to use instead.

I would start with submitting a patch to coreutils, if you can figure
out that code enough to do so (I find it quite opaque). Since it has
been in the kernel for a while already, it should be acceptable to the
upstream coreutils maintainers to use this interface. Doubly so if you
include some benchmarks with CIFS/NFS clients avoiding network overhead
during the copy.

Cheers, Andreas

[Andreas Dilger via samba-technical]

Post by Andreas Dilger via samba-technical

Post by Steve French via samba-technical
Are there any user space tools (other than our test tools and xfs_io
etc.) that support copy_file_range? Looks like at least cp and rsync
and dd don't. That syscall which now has been around a couple years,
and was reminded about at the LSF/MM summit a few days ago, presumably
is the 'best' way to copy a file fast since it tries all the
mechanisms (reflink etc.) in order.
Since copy_file_range syscall can be 100x or more faster for network
file systems than the alternative, was surprised when I noticed that
cp and rsync didn't support it. It doesn't look like rsync even
supports reflink either(although presumably if you call
copy_file_range you don't have to worry about that), and reads/writes
are 8K. See copy_file() in rsync/util.c
In the cp command it looks like it can call the FICLONE IOCTL (see
clone_file() in coreutils/src/copy.c) but doesn't call the expected
"copy_file_range" syscall.
In the dd command it doesn't call either - see dd_copy in corutils/src/dd.c
Since it can be 100x or more faster in some cases to call
copy_file_range than do reads/writes back and forth to do a copy
(especially if network or clustered backend or cloud), what tools are
the best to recommend?
Would rsync or cp be likely to take patches to call the standard
"copy_file_range" syscall
(http://man7.org/linux/man-pages/man2/copy_file_range.2.html)?
Presumably not if it has been two+ years ... but would be interested
what copy tools to recommend to use instead.

I would start with submitting a patch to coreutils, if you can figure
out that code enough to do so (I find it quite opaque). Since it has
been in the kernel for a while already, it should be acceptable to the
upstream coreutils maintainers to use this interface. Doubly so if you
include some benchmarks with CIFS/NFS clients avoiding network overhead
during the copy.

For cp (coreutils), apparently there was a concern that copy_file_range()
expands holes; see the thread at
https://lists.gnu.org/archive/html/bug-coreutils/2016-09/msg00020.html.
Though, I'd think it could just be used on non-holes only. And I don't think
the size_t type of 'len' is a problem either, since it's the copy length, not
the file size. You just call it multiple times if the file is larger.

I think cp is already using SEEK_HOLE/SEEK_DATA and/or FIEMAP to determine
the mapped and sparse segments of the file, so it should be practical to
use copy_file_range() in conjunction with these to copy only the allocated
parts of the file.

Cheers, Andreas

[Steve French via samba-technical]

Post by Andreas Dilger via samba-technical

Post by Andreas Dilger via samba-technical

Post by Steve French via samba-technical
Are there any user space tools (other than our test tools and xfs_io
etc.) that support copy_file_range? Looks like at least cp and rsync
and dd don't. That syscall which now has been around a couple years,
and was reminded about at the LSF/MM summit a few days ago, presumably
is the 'best' way to copy a file fast since it tries all the
mechanisms (reflink etc.) in order.
Since copy_file_range syscall can be 100x or more faster for network
file systems than the alternative, was surprised when I noticed that
cp and rsync didn't support it. It doesn't look like rsync even
supports reflink either(although presumably if you call
copy_file_range you don't have to worry about that), and reads/writes
are 8K. See copy_file() in rsync/util.c
In the cp command it looks like it can call the FICLONE IOCTL (see
clone_file() in coreutils/src/copy.c) but doesn't call the expected
"copy_file_range" syscall.
In the dd command it doesn't call either - see dd_copy in corutils/src/dd.c
Since it can be 100x or more faster in some cases to call
copy_file_range than do reads/writes back and forth to do a copy
(especially if network or clustered backend or cloud), what tools are
the best to recommend?
Would rsync or cp be likely to take patches to call the standard
"copy_file_range" syscall
(http://man7.org/linux/man-pages/man2/copy_file_range.2.html)?
Presumably not if it has been two+ years ... but would be interested
what copy tools to recommend to use instead.

I would start with submitting a patch to coreutils, if you can figure
out that code enough to do so (I find it quite opaque). Since it has
been in the kernel for a while already, it should be acceptable to the
upstream coreutils maintainers to use this interface. Doubly so if you
include some benchmarks with CIFS/NFS clients avoiding network overhead
during the copy.

For cp (coreutils), apparently there was a concern that copy_file_range()
expands holes; see the thread at
https://lists.gnu.org/archive/html/bug-coreutils/2016-09/msg00020.html.
Though, I'd think it could just be used on non-holes only. And I don't think
the size_t type of 'len' is a problem either, since it's the copy length, not
the file size. You just call it multiple times if the file is larger.

I think cp is already using SEEK_HOLE/SEEK_DATA and/or FIEMAP to determine
the mapped and sparse segments of the file, so it should be practical to
use copy_file_range() in conjunction with these to copy only the allocated
parts of the file.

For the case where clone/reflink or copy_file_range is supported - is
there any reason to
not sent the request to copy the whole file? Presumably long
timeout/errors might be a concern, but
that could happen with ranges too. In any case, if sent the whole
file copy request,
the server file system can figure out the holes and copy more efficiently.

In the case where it is copying local to remote or remote to local -
figuring out whether it is
sparse and optimizing makes a lot of sense - but I didn't think cp did
that (at least the
sections of code I was looking at).