Re: [dm-devel] [PATCH 0/7] add simple copy support

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Aug 17, 2021 at 03:44:16PM +0530, SelvaKumar S wrote:
> This started out as an attempt to support NVMe Simple Copy Command (SCC),
> and evolved during the RFC review process.
> 
> The patchset, at this point, contains -
> 1. SCC support in NVMe driver
> 2. Block-layer infra for copy-offload operation
> 3. ioctl interface to user-space
> 4. copy-emulation infra in the block-layer
> 5. copy-offload plumbing to dm-kcopyd (thus creating couple of in-kernel
> 	users such as dm-clone)
> 
> 
> The SCC specification, i.e. TP4065a can be found in following link
> 
> https://nvmexpress.org/wp-content/uploads/NVM-Express-1.4-Ratified-TPs.zip
> 
> Simple copy is a copy offloading feature and can be 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.
> 
> We define a block ioctl for copy and copy payload format similar to
> discard. For device supporting native simple copy, we attach the control
> information as payload to the bio and submit to the device. Copy emulation
> is implemented incase underlaying device does not support copy offload or
> based on sysfs choice. Copy emulation is done by reading each source range
> into buffer and writing it to the destination.

Seems useful.  Would you mind adapting the loop driver to call
copy_file_range (for files) so that anyone interested in making a
filesystem use this capability (cough) can write fstests?

--D

> At present this implementation does not support copy offload for stacked/dm
> devices, rather copy operation is completed through emulation.
> 
> One of the in-kernel use case for copy-offload is implemented by this
> patchset. dm-kcopyd infra has been changed to leverage the copy-offload if
> it is natively available. Other future use-cases could be F2FS GC, BTRFS
> relocation/balance and copy_file_range.
> 
> Following limits are added to queue limits and are exposed via sysfs to
> userspace, which user can use to form a payload.
> 
>  - copy_offload:
> 	configurable, can be used set emulation or copy offload
> 		0 to disable copy offload,
> 		1 to enable copy offloading support. Offload can be only
> 			enabled, if underlaying device supports offload
> 
>  - max_copy_sectors:
> 	total copy length supported by copy offload feature in device.
> 	0 indicates copy offload is not supported.
> 
>  - max_copy_nr_ranges:
> 	maximum number of source range entries supported by copy offload
> 			feature in device
> 
>  - max_copy_range_sectors:
> 	maximum copy length per source range entry
> 
> *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 queue parameter
> copy_offload is 1, then copy is done through native copy offloading.
> Copy emulation is used in otherwise.
> 
> Changes from  RFC v5
> 
> 1. Handle copy larger than maximum copy limits
> 2. Create copy context and submit copy offload asynchronously
> 3. Remove BLKDEV_COPY_NOEMULATION opt-in option of copy offload and
> check for copy support before submission from dm and other layers
> 4. Allocate maximum possible allocatable buffer for copy emulation
> rather failing very large copy offload.
> 5. Fix copy_offload sysfs to be either have 0 or 1
> 
> Changes from RFC 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()
> 
> Changes from RFC 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 RFC 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 RFC 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
> 
> 
> Nitesh Shetty (4):
>   block: Introduce queue limits for copy-offload support
>   block: copy offload support infrastructure
>   block: Introduce a new ioctl for simple copy
>   block: add emulation for simple copy
> 
> SelvaKumar S (3):
>   block: make bio_map_kern() non static
>   nvme: add simple copy support
>   dm kcopyd: add simple copy offload support
> 
>  block/blk-core.c          |  84 ++++++++-
>  block/blk-lib.c           | 352 ++++++++++++++++++++++++++++++++++++++
>  block/blk-map.c           |   2 +-
>  block/blk-settings.c      |   4 +
>  block/blk-sysfs.c         |  51 ++++++
>  block/blk-zoned.c         |   1 +
>  block/bounce.c            |   1 +
>  block/ioctl.c             |  33 ++++
>  drivers/md/dm-kcopyd.c    |  56 +++++-
>  drivers/nvme/host/core.c  |  83 +++++++++
>  drivers/nvme/host/trace.c |  19 ++
>  include/linux/bio.h       |   1 +
>  include/linux/blk_types.h |  20 +++
>  include/linux/blkdev.h    |  21 +++
>  include/linux/nvme.h      |  43 ++++-
>  include/uapi/linux/fs.h   |  20 +++
>  16 files changed, 775 insertions(+), 16 deletions(-)
> 
> -- 
> 2.25.1
> 

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