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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