On Apr 27, 2018, at 12:25 PM, Steve French <smfrench@xxxxxxxxx> wrote: > > 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
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