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

[Damien Le Moal]

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