[PATCH v8 0/9] Implement copy offload support

Anuj Gupta
2023-03-29T08:16:19Z

From: Nitesh Shetty <nj.shetty@samsung.com>

The patch series covers the points discussed in November 2021 virtual
call [LSF/MM/BFP TOPIC] Storage: Copy Offload [0].
We have covered the initial agreed requirements in this patchset and
further additional features suggested by community.
Patchset borrows Mikulas's token based approach for 2 bdev
implementation.

This is on top of our previous patchset v7[1].

Overall series supports:
========================
1. Driver
- NVMe Copy command (single NS, TP 4065), including support
in nvme-target (for block and file backend).

2. Block layer
- Block-generic copy (REQ_COPY flag), with interface
accommodating two block-devs
- Emulation, for in-kernel user when offload is natively
absent
- dm-linear support (for cases not requiring split)

3. User-interface
- copy_file_range

Testing
=======
Copy offload can be tested on:
a. QEMU: NVME simple copy (TP 4065). By setting nvme-ns
parameters mssrl,mcl, msrc. For more info [2].
b. Null block device
c. Fabrics loopback.
d. blktests[3] (tests block/032,033, nvme/046,047,048,049)

Emulation can be tested on any device.

fio[4].

Infra and plumbing:
===================
We populate copy_file_range callback in def_blk_fops.
For devices that support copy-offload, use blkdev_copy_offload to
achieve in-device copy.
However for cases, where device doesn't support offload,
fallback to generic_copy_file_range.
For in-kernel users (like fabrics), we use blkdev_issue_copy
which implements its own emulation, as fd is not available.
Modify checks in generic_copy_file_range to support block-device.

Performance:
============
The major benefit of this copy-offload/emulation framework is
observed in fabrics setup, for copy workloads across the network.
The host will send offload command over the network and actual copy
can be achieved using emulation on the target.
This results in better performance and network utilisation,
as compared to read and write travelling across the network.
With async-design of copy-offload/emulation we are able to see the
following improvements as compared to userspace read + write on a
NVMeOF TCP setup:

Setup1: Network Speed: 1000Mb/s
Host PC: Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
Target PC: AMD Ryzen 9 5900X 12-Core Processor
block size 8k:
710% improvement in IO BW (108 MiB/s to 876 MiB/s).
Network utilisation drops from 97% to 15%.
block-size 1M:
2532% improvement in IO BW (101 MiB/s to 2659 MiB/s).
Network utilisation drops from 89% to 0.62%.

Setup2: Network Speed: 100Gb/s
Server: Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz, 72 cores
(host and target have the same configuration)
block-size 8k:
17.5% improvement in IO BW (794 MiB/s to 933 MiB/s).
Network utilisation drops from 6.75% to 0.16%.

Blktests[3]
======================
tests/block/032,033: Runs copy offload and emulation on block device.
tests/nvme/046,047,048,049 Create a loop backed fabrics device and
run copy offload and emulation.

Future Work
===========
- loopback device copy offload support
- upstream fio to use copy offload

These are to be taken up after we reach consensus on the
plumbing of current elements that are part of this series.

Additional links:
=================
[0] https://lore.kernel.org/linux-nvme/CA+1E3rJ7BZ7LjQXXTdX+-0Edz=zT14mmPGMiVCzUgB33C60tbQ@mail.gmail.com/
[1] https://lore.kernel.org/lkml/20230220105336.3810-1-nj.shetty@samsung.com/
[2] https://qemu-project.gitlab.io/qemu/system/devices/nvme.html#simple-copy
[3] https://github.com/nitesh-shetty/blktests/tree/feat/copy_offload/v7
[4] https://github.com/vincentkfu/fio/tree/copyoffload-cfr-3.33-v7

Changes since v7:
=================
- null block copy offload support for testing (Damien Le Moal)
- adding direct flag check for copy offload to block device,
as we are using generic_copy_file_range for cached cases.
- Minor fixes

Changes since v6:
=================
- copy_file_range instead of ioctl for direct block device
- Remove support for multi range (vectored) copy
- Remove ioctl interface for copy.
- Remove offload support in dm kcopyd.

Changes since v5:
=================
- Addition of blktests (Chaitanya Kulkarni)
- Minor fix for fabrics file backed path
- Remove buggy zonefs copy file range implementation.

Changes since v4:
=================
- make the offload and emulation design asynchronous (Hannes
Reinecke)
- fabrics loopback support
- sysfs naming improvements (Damien Le Moal)
- use kfree() instead of kvfree() in cio_await_completion
(Damien Le Moal)
- use ranges instead of rlist to represent range_entry (Damien
Le Moal)
- change argument ordering in blk_copy_offload suggested (Damien
Le Moal)
- removed multiple copy limit and merged into only one limit
(Damien Le Moal)
- wrap overly long lines (Damien Le Moal)
- other naming improvements and cleanups (Damien Le Moal)
- correctly format the code example in description (Damien Le
Moal)
- mark blk_copy_offload as static (kernel test robot)

Changes since v3:
=================
- added copy_file_range support for zonefs
- added documentation about new sysfs entries
- incorporated review comments on v3
- minor fixes

Changes since v2:
=================
- fixed possible race condition reported by Damien Le Moal
- new sysfs controls as suggested by Damien Le Moal
- fixed possible memory leak reported by Dan Carpenter, lkp
- minor fixes

Nitesh Shetty (9):
block: Introduce queue limits for copy-offload support
block: Add copy offload support infrastructure
block: add emulation for copy
fs, block: copy_file_range for def_blk_ops for direct block device.
nvme: add copy offload support
nvmet: add copy command support for bdev and file ns
dm: Add support for copy offload.
dm: Enable copy offload for dm-linear target
null_blk: add support for copy offload

Documentation/ABI/stable/sysfs-block | 36 +++
block/blk-lib.c | 427 +++++++++++++++++++++++++++
block/blk-map.c | 4 +-
block/blk-settings.c | 24 ++
block/blk-sysfs.c | 64 ++++
block/blk.h | 2 +
block/fops.c | 20 ++
drivers/block/null_blk/main.c | 94 ++++++
drivers/block/null_blk/null_blk.h | 7 +
drivers/md/dm-linear.c | 1 +
drivers/md/dm-table.c | 42 +++
drivers/md/dm.c | 7 +
drivers/nvme/host/constants.c | 1 +
drivers/nvme/host/core.c | 106 ++++++-
drivers/nvme/host/fc.c | 5 +
drivers/nvme/host/nvme.h | 7 +
drivers/nvme/host/pci.c | 27 +-
drivers/nvme/host/rdma.c | 7 +
drivers/nvme/host/tcp.c | 16 +
drivers/nvme/host/trace.c | 19 ++
drivers/nvme/target/admin-cmd.c | 9 +-
drivers/nvme/target/io-cmd-bdev.c | 58 ++++
drivers/nvme/target/io-cmd-file.c | 52 ++++
drivers/nvme/target/loop.c | 6 +
drivers/nvme/target/nvmet.h | 1 +
fs/read_write.c | 11 +-
include/linux/blk_types.h | 25 ++
include/linux/blkdev.h | 21 ++
include/linux/device-mapper.h | 5 +
include/linux/nvme.h | 43 ++-
include/uapi/linux/fs.h | 3 +
31 files changed, 1136 insertions(+), 14 deletions(-)

base-commit: 0aa250ce67a2697327415132a0aa4e9f1f0fe000
--
2.35.1.500.gb896f729e2