Re: [RFC PATCH v2 0/2] add simple copy support

Damien Le Moal
2020-12-04T11:25:27Z

On 2020/12/04 20:02, SelvaKumar S wrote:
> 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
>
> This is an RFC. Looking forward for any feedbacks or other alternate
> designs for plumbing simple copy to IO stack.
>
> 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 accepts destination, no of sources and arrays of
> source ranges from application and attach it as payload to the bio and
> submits to the device.
>
> Following limits are added to queue limits and are exposed in sysfs
> to userspace
> - *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.

Same comment as before. I think this is a good start, but for this to be really
useful to users and kernel components alike, this really needs copy emulation
for drives that do not have a native copy feature, similarly to what write zeros
handling for instance: if the drive does not have a copy command (simple copy
for NVMe or XCOPY for scsi), then the block layer should issue read/write
commands to seamlessly execute the copy. Otherwise, this will only serve a small
niche for users and will not be optimal for FS and DM drivers that could be
simplified with a generic block layer copy functionality.

This is my 10 cents though, others may differ about this.

>
> 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 (2):
> block: add simple copy support
> nvme: add simple copy support
>
> block/blk-core.c | 94 ++++++++++++++++++++++++++---
> block/blk-lib.c | 123 ++++++++++++++++++++++++++++++++++++++
> block/blk-merge.c | 2 +
> block/blk-settings.c | 11 ++++
> block/blk-sysfs.c | 23 +++++++
> block/blk-zoned.c | 1 +
> block/bounce.c | 1 +
> block/ioctl.c | 43 +++++++++++++
> drivers/nvme/host/core.c | 87 +++++++++++++++++++++++++++
> include/linux/bio.h | 1 +
> include/linux/blk_types.h | 15 +++++
> include/linux/blkdev.h | 15 +++++
> include/linux/nvme.h | 43 ++++++++++++-
> include/uapi/linux/fs.h | 13 ++++
> 14 files changed, 461 insertions(+), 11 deletions(-)
>

--
Damien Le Moal
Western Digital Research