[RFC PATCH v5 0/4] add simple copy support

SelvaKumar S
2021-02-20T02:02:50Z

This patchset tries to add support for TP4065a ("Simple Copy Command"),
v2020.05.04 ("Ratified")

The Specification can be found in following link.
https://nvmexpress.org/wp-content/uploads/NVM-Express-1.4-Ratified-TPs-1.zip

Simple copy command is a copy offloading operation and is used to copy
multiple contiguous ranges (source_ranges) of LBA's to a single destination
LBA within the device reducing traffic between host and device.

This implementation doesn't add native copy offload support for stacked
devices rather copy offload is done through emulation. Possible use
cases are F2FS gc and BTRFS relocation/balance.

*blkdev_issue_copy* takes source bdev, no of sources, array of source
ranges (in sectors), destination bdev and destination offset(in sectors).
If both source and destination block devices are same and copy_offload = 1,
then copy is done through native copy offloading. Copy emulation is used
in other cases.

As SCSI XCOPY can take two different block devices and no of source range is
equal to 1, this interface can be extended in future to support SCSI XCOPY.

For devices supporting native simple copy, attach the control information
as payload to the bio and submit to the device. For devices without native
copy support, copy emulation is done by reading each source range into memory
and writing it to the destination. Caller can choose not to try
emulation if copy offload is not supported by setting
BLKDEV_COPY_NOEMULATION flag.

Following limits are added to queue limits and are exposed in sysfs
to userspace
- *copy_offload* controls copy_offload. set 0 to disable copy
offload, 1 to enable native copy offloading support.
- *max_copy_sectors* limits the sum of all source_range length
- *max_copy_nr_ranges* limits the number of source ranges
- *max_copy_range_sectors* limit the maximum number of sectors
that can constitute a single source range.

max_copy_sectors = 0 indicates the device doesn't support copy
offloading.

*copy offload* sysfs entry is configurable and can be used toggle
between emulation and native support depending upon the usecase.

Changes from v4

1. Extend dm-kcopyd to leverage copy-offload, while copying within the
same device. The other approach was to have copy-emulation by moving
dm-kcopyd to block layer. But it also required moving core dm-io infra,
causing a massive churn across multiple dm-targets.

2. Remove export in bio_map_kern()
3. Change copy_offload sysfs to accept 0 or else
4. Rename copy support flag to QUEUE_FLAG_SIMPLE_COPY
5. Rename payload entries, add source bdev field to be used while
partition remapping, remove copy_size
6. Change the blkdev_issue_copy() interface to accept destination and
source values in sector rather in bytes
7. Add payload to bio using bio_map_kern() for copy_offload case
8. Add check to return error if one of the source range length is 0
9. Add BLKDEV_COPY_NOEMULATION flag to allow user to not try copy
emulation incase of copy offload is not supported. Caller can his use
his existing copying logic to complete the io.
10. Bug fix copy checks and reduce size of rcu_lock()

Planned for next:
- adding blktests
- handling larger (than device limits) copy
- decide on ioctl interface (man-page etc.)

Changes from v3

1. gfp_flag fixes.
2. Export bio_map_kern() and use it to allocate and add pages to bio.
3. Move copy offload, reading to buf, writing from buf to separate functions.
4. Send read bio of copy offload by chaining them and submit asynchronously.
5. Add gendisk->part0 and part->bd_start_sect changes to blk_check_copy().
6. Move single source range limit check to blk_check_copy()
7. Rename __blkdev_issue_copy() to blkdev_issue_copy and remove old helper.
8. Change blkdev_issue_copy() interface generic to accepts destination bdev
to support XCOPY as well.
9. Add invalidate_kernel_vmap_range() after reading data for vmalloc'ed memory.
10. Fix buf allocoation logic to allocate buffer for the total size of copy.
11. Reword patch commit description.

Changes from v2

1. Add emulation support for devices not supporting copy.
2. Add *copy_offload* sysfs entry to enable and disable copy_offload
in devices supporting simple copy.
3. Remove simple copy support for stacked devices.

Changes from v1:

1. Fix memory leak in __blkdev_issue_copy
2. Unmark blk_check_copy inline
3. Fix line break in blk_check_copy_eod
4. Remove p checks and made code more readable
5. Don't use bio_set_op_attrs and remove op and set
bi_opf directly
6. Use struct_size to calculate total_size
7. Fix partition remap of copy destination
8. Remove mcl,mssrl,msrc from nvme_ns
9. Initialize copy queue limits to 0 in nvme_config_copy
10. Remove return in QUEUE_FLAG_COPY check
11. Remove unused OCFS

SelvaKumar S (4):
block: make bio_map_kern() non static
block: add simple copy support
nvme: add simple copy support
dm kcopyd: add simple copy offload support

block/blk-core.c | 102 +++++++++++++++--
block/blk-lib.c | 223 ++++++++++++++++++++++++++++++++++++++
block/blk-map.c | 2 +-
block/blk-merge.c | 2 +
block/blk-settings.c | 10 ++
block/blk-sysfs.c | 47 ++++++++
block/blk-zoned.c | 1 +
block/bounce.c | 1 +
block/ioctl.c | 33 ++++++
drivers/md/dm-kcopyd.c | 49 ++++++++-
drivers/nvme/host/core.c | 87 +++++++++++++++
include/linux/bio.h | 1 +
include/linux/blk_types.h | 14 +++
include/linux/blkdev.h | 17 +++
include/linux/nvme.h | 43 +++++++-
include/uapi/linux/fs.h | 13 +++
16 files changed, 627 insertions(+), 18 deletions(-)

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2.25.1