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

Nitesh Shetty
2021-08-18T15:40:47Z

On Wed, Aug 18, 2021 at 5:07 AM Darrick J. Wong <djwong@kernel.org> wrote:
>
> 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?

We are planning to look into copy_file_range plumbing after settling
on the current series,
which already became heavyweight for the first drop.

Nitesh Shetty
>
> --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
> >