[PATCH v1 0/8] VFS: In-kernel copy system call

[Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>]

Copy system calls came up during Plumbers a couple of weeks ago, because
several filesystems (including NFS and XFS) are currently working on copy
acceleration implementations.  We haven't heard from Zach Brown in a while,
so I volunteered to push his patches upstream so individual filesystems
don't need to keep writing their own ioctls.

The first three patches are a simple reposting of Zach's patches from several
months ago, with one minor error code fix.  The remaining patches add in a
fallback mechanism when filesystems don't provide a copy function.  This is
especially useful when doing a server-side copy on NFS (using the new COPY
operation in NFS v4.2).  This fallback can be disabled by passing the flag
COPY_REFLINK to the system call.

The last patch is a man page patch documenting this new system call,
including an example program.

I tested the fallback option by using /dev/urandom to generate files of
varying sizes and copying them.  I compared the time to copy against that
of `cp` just to see if there is a noticable difference.  I found that
runtimes are roughly the same, but in-kernel copy tends to use less of
the cpu.  Values in the tables below are averages across multiple trials.


 /usr/bin/cp |   512 MB  |   1024 MB |   1536 MB |   2048 MB
-------------|-----------|-----------|-----------|-----------
       user  |   0.00s   |   0.00s   |   0.00s   |   0.00s
     system  |   0.32s   |   0.52s   |   1.04s   |   1.04s
        cpu  |     73%   |     69%   |     62%   |     62%
      total  |   0.446   |   0.757   |   1.197   |   1.667


   VFS copy  |   512 MB  |   1024 MB |   1536 MB |   2048 MB
-------------|-----------|-----------|-----------|-----------
       user  |   0.00s   |   0.00s   |   0.00s   |  0.00s
     system  |   0.33s   |   0.49s   |   0.76s   |  0.99s
        cpu  |     77%   |     62%   |     60%   |    59%
      total  |   0.422   |   0.777   |   1.267   |  1.655


Questions?  Comments?  Thoughts?

Anna


Anna Schumaker (5):
  btrfs: Add mountpoint checking during btrfs_copy_file_range
  vfs: Remove copy_file_range mountpoint checks
  vfs: Copy should check len after file open mode
  vfs: Copy should use file_out rather than file_in
  vfs: Fall back on splice if no copy function defined

Zach Brown (3):
  vfs: add copy_file_range syscall and vfs helper
  x86: add sys_copy_file_range to syscall tables
  btrfs: add .copy_file_range file operation

 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 fs/btrfs/ctree.h                       |   3 +
 fs/btrfs/file.c                        |   1 +
 fs/btrfs/ioctl.c                       |  95 ++++++++++++++----------
 fs/read_write.c                        | 132 +++++++++++++++++++++++++++++++++
 include/linux/copy.h                   |   6 ++
 include/linux/fs.h                     |   3 +
 include/uapi/asm-generic/unistd.h      |   4 +-
 include/uapi/linux/Kbuild              |   1 +
 include/uapi/linux/copy.h              |   6 ++
 kernel/sys_ni.c                        |   1 +
 12 files changed, 214 insertions(+), 40 deletions(-)
 create mode 100644 include/linux/copy.h
 create mode 100644 include/uapi/linux/copy.h

-- 
2.5.1

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