[dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Chaitanya Kulkarni]

Hi,

* Background :-
-----------------------------------------------------------------------

Copy offload is a feature that allows file-systems or storage devices
to be instructed to copy files/logical blocks without requiring
involvement of the local CPU.

With reference to the RISC-V summit keynote [1] single threaded
performance is limiting due to Denard scaling and multi-threaded
performance is slowing down due Moore's law limitations. With the rise
of SNIA Computation Technical Storage Working Group (TWG) [2],
offloading computations to the device or over the fabrics is becoming
popular as there are several solutions available [2]. One of the common
operation which is popular in the kernel and is not merged yet is Copy
offload over the fabrics or on to the device.

* Problem :-
-----------------------------------------------------------------------

The original work which is done by Martin is present here [3]. The
latest work which is posted by Mikulas [4] is not merged yet. These two
approaches are totally different from each other. Several storage
vendors discourage mixing copy offload requests with regular READ/WRITE
I/O. Also, the fact that the operation fails if a copy request ever
needs to be split as it traverses the stack it has the unfortunate
side-effect of preventing copy offload from working in pretty much
every common deployment configuration out there.

* Current state of the work :-
-----------------------------------------------------------------------

With [3] being hard to handle arbitrary DM/MD stacking without
splitting the command in two, one for copying IN and one for copying
OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
candidate. Also, with [4] there is an unresolved problem with the
two-command approach about how to handle changes to the DM layout
between an IN and OUT operations.

* Why Linux Kernel Storage System needs Copy Offload support now ?
-----------------------------------------------------------------------

With the rise of the SNIA Computational Storage TWG and solutions [2],
existing SCSI XCopy support in the protocol, recent advancement in the
Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
DMA support in the Linux Kernel mainly for NVMe devices [7] and
eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
from Copy offload operation.

With this background we have significant number of use-cases which are
strong candidates waiting for outstanding Linux Kernel Block Layer Copy
Offload support, so that Linux Kernel Storage subsystem can to address
previously mentioned problems [1] and allow efficient offloading of the
data related operations. (Such as move/copy etc.)

For reference following is the list of the use-cases/candidates waiting
for Copy Offload support :-

1. SCSI-attached storage arrays.
2. Stacking drivers supporting XCopy DM/MD.
3. Computational Storage solutions.
7. File systems :- Local, NFS and Zonefs.
4. Block devices :- Distributed, local, and Zoned devices.
5. Peer to Peer DMA support solutions.
6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.

* What we will discuss in the proposed session ?
-----------------------------------------------------------------------

I'd like to propose a session to go over this topic to understand :-

1. What are the blockers for Copy Offload implementation ?
2. Discussion about having a file system interface.
3. Discussion about having right system call for user-space.
4. What is the right way to move this work forward ?
5. How can we help to contribute and move this work forward ?

* Required Participants :-
-----------------------------------------------------------------------

I'd like to invite file system, block layer, and device drivers
developers to:-

1. Share their opinion on the topic.
2. Share their experience and any other issues with [4].
3. Uncover additional details that are missing from this proposal.

Required attendees :-

Martin K. Petersen
Jens Axboe
Christoph Hellwig
Bart Van Assche
Zach Brown
Roland Dreier
Ric Wheeler
Trond Myklebust
Mike Snitzer
Keith Busch
Sagi Grimberg
Hannes Reinecke
Frederick Knight
Mikulas Patocka
Keith Busch

Regards,
Chaitanya

[1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
[2] https://www.snia.org/computational
https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
      https://www.eideticom.com/products.html
https://www.xilinx.com/applications/data-center/computational-storage.html
[3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
[4] https://www.spinics.net/lists/linux-block/msg00599.html
[5] https://lwn.net/Articles/793585/
[6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
namespaces-zns-as-go-to-industry-technology/
[7] https://github.com/sbates130272/linux-p2pmem
[8] https://kernel.dk/io_uring.pdf




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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Knight, Frederick]

I'd love to participate in this discussion.

You mention the 2 different models (single command vs. multi-command).  Just as a reminder, there are specific reasons for those 2 different models.

Some applications know both the source and the destination, so can use the single command model (the application is aware it is doing a copy).  But, there is a group of applications that do NOT know both pieces of information at the same time, in the same thread, in the same context (the application is NOT aware it is doing a copy - the application thinks it is doing reads and writes).

That is why there are 2 different models - because the application engineers didn't want to change their application.  So, the author of the CP application (the shell copy command) wanted to use the existing READ / WRITE model (2 commands).  Just replace the READ with "get the data ready" and replace the WRITE with "use the data you got ready".  It was easier for that application to use the existing model, rather than totally redesigning the application.

But, other application engineers had a code base that already knew a copy was happening, and their code already knew both the source and destination in the same code path. A BACKUP application is one that generally fits into this camp.  So, it was easier for that application to replace that function with a single copy request.  Another application was a VM mastering/replicating application that could spin up new VM images very quickly - the source and destination are known to be able to use a single request.

When this offload journey began, both interfaces were needed and used.  But yes, it did bifurcate the space, creating 2 camps of engineers - each with their favorite method (based on the application where they planned to use it).  Each camp of engineers often sees no reason that the other camp can't just switch to do it the way they do - if they'd only see the light.  But, originally, there were 2 different sets of requirements that each drove a specific design of a copy offload model.

Even NVMe has recently joined the copy offload camp with a new COPY command (single namespace, multiple source ranges, single destination range - works well for defrag, and other use cases). I'm confident its capabilities will grow over time.

SO, I think this will be a great discussion to have!!!

	Fred Knight



-----Original Message-----
From: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com> 
Sent: Monday, May 10, 2021 8:16 PM
To: linux-block@vger.kernel.org; linux-scsi@vger.kernel.org; linux-nvme@lists.infradead.org; dm-devel@redhat.com; lsf-pc@lists.linux-foundation.org
Cc: axboe@kernel.dk; msnitzer@redhat.com; bvanassche@acm.org; martin.petersen@oracle.com; roland@purestorage.com; mpatocka@redhat.com; Hannes Reinecke <hare@suse.de>; kbusch@kernel.org; rwheeler@redhat.com; hch@lst.de; Knight, Frederick <Frederick.Knight@netapp.com>; zach.brown@ni.com; osandov@fb.com
Subject: [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

NetApp Security WARNING: This is an external email. Do not click links or open attachments unless you recognize the sender and know the content is safe.




Hi,

* Background :-
-----------------------------------------------------------------------

Copy offload is a feature that allows file-systems or storage devices to be instructed to copy files/logical blocks without requiring involvement of the local CPU.

With reference to the RISC-V summit keynote [1] single threaded performance is limiting due to Denard scaling and multi-threaded performance is slowing down due Moore's law limitations. With the rise of SNIA Computation Technical Storage Working Group (TWG) [2], offloading computations to the device or over the fabrics is becoming popular as there are several solutions available [2]. One of the common operation which is popular in the kernel and is not merged yet is Copy offload over the fabrics or on to the device.

* Problem :-
-----------------------------------------------------------------------

The original work which is done by Martin is present here [3]. The latest work which is posted by Mikulas [4] is not merged yet. These two approaches are totally different from each other. Several storage vendors discourage mixing copy offload requests with regular READ/WRITE I/O. Also, the fact that the operation fails if a copy request ever needs to be split as it traverses the stack it has the unfortunate side-effect of preventing copy offload from working in pretty much every common deployment configuration out there.

* Current state of the work :-
-----------------------------------------------------------------------

With [3] being hard to handle arbitrary DM/MD stacking without splitting the command in two, one for copying IN and one for copying OUT. Which is then demonstrated by the [4] why [3] it is not a suitable candidate. Also, with [4] there is an unresolved problem with the two-command approach about how to handle changes to the DM layout between an IN and OUT operations.

* Why Linux Kernel Storage System needs Copy Offload support now ?
-----------------------------------------------------------------------

With the rise of the SNIA Computational Storage TWG and solutions [2], existing SCSI XCopy support in the protocol, recent advancement in the Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer DMA support in the Linux Kernel mainly for NVMe devices [7] and eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit from Copy offload operation.

With this background we have significant number of use-cases which are strong candidates waiting for outstanding Linux Kernel Block Layer Copy Offload support, so that Linux Kernel Storage subsystem can to address previously mentioned problems [1] and allow efficient offloading of the data related operations. (Such as move/copy etc.)

For reference following is the list of the use-cases/candidates waiting for Copy Offload support :-

1. SCSI-attached storage arrays.
2. Stacking drivers supporting XCopy DM/MD.
3. Computational Storage solutions.
7. File systems :- Local, NFS and Zonefs.
4. Block devices :- Distributed, local, and Zoned devices.
5. Peer to Peer DMA support solutions.
6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.

* What we will discuss in the proposed session ?
-----------------------------------------------------------------------

I'd like to propose a session to go over this topic to understand :-

1. What are the blockers for Copy Offload implementation ?
2. Discussion about having a file system interface.
3. Discussion about having right system call for user-space.
4. What is the right way to move this work forward ?
5. How can we help to contribute and move this work forward ?

* Required Participants :-
-----------------------------------------------------------------------

I'd like to invite file system, block layer, and device drivers developers to:-

1. Share their opinion on the topic.
2. Share their experience and any other issues with [4].
3. Uncover additional details that are missing from this proposal.

Required attendees :-

Martin K. Petersen
Jens Axboe
Christoph Hellwig
Bart Van Assche
Zach Brown
Roland Dreier
Ric Wheeler
Trond Myklebust
Mike Snitzer
Keith Busch
Sagi Grimberg
Hannes Reinecke
Frederick Knight
Mikulas Patocka
Keith Busch

Regards,
Chaitanya

[1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
[2] https://www.snia.org/computational
https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
      https://www.eideticom.com/products.html
https://www.xilinx.com/applications/data-center/computational-storage.html
[3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy [4] https://www.spinics.net/lists/linux-block/msg00599.html
[5] https://lwn.net/Articles/793585/
[6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
namespaces-zns-as-go-to-industry-technology/
[7] https://github.com/sbates130272/linux-p2pmem
[8] https://kernel.dk/io_uring.pdf


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 5/10/21 5:15 PM, Chaitanya Kulkarni wrote:
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?

Are there any blockers left? My understanding is that what is needed is
to implement what has been proposed recently
(https://lore.kernel.org/linux-nvme/yq1blf3smcl.fsf@ca-mkp.ca.oracle.com/).
Anyway, I'm interested to attend the conversation about this topic.

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 11.05.2021 00:15, Chaitanya Kulkarni wrote:
>Hi,
>
>* Background :-
>-----------------------------------------------------------------------
>
>Copy offload is a feature that allows file-systems or storage devices
>to be instructed to copy files/logical blocks without requiring
>involvement of the local CPU.
>
>With reference to the RISC-V summit keynote [1] single threaded
>performance is limiting due to Denard scaling and multi-threaded
>performance is slowing down due Moore's law limitations. With the rise
>of SNIA Computation Technical Storage Working Group (TWG) [2],
>offloading computations to the device or over the fabrics is becoming
>popular as there are several solutions available [2]. One of the common
>operation which is popular in the kernel and is not merged yet is Copy
>offload over the fabrics or on to the device.
>
>* Problem :-
>-----------------------------------------------------------------------
>
>The original work which is done by Martin is present here [3]. The
>latest work which is posted by Mikulas [4] is not merged yet. These two
>approaches are totally different from each other. Several storage
>vendors discourage mixing copy offload requests with regular READ/WRITE
>I/O. Also, the fact that the operation fails if a copy request ever
>needs to be split as it traverses the stack it has the unfortunate
>side-effect of preventing copy offload from working in pretty much
>every common deployment configuration out there.
>
>* Current state of the work :-
>-----------------------------------------------------------------------
>
>With [3] being hard to handle arbitrary DM/MD stacking without
>splitting the command in two, one for copying IN and one for copying
>OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
>candidate. Also, with [4] there is an unresolved problem with the
>two-command approach about how to handle changes to the DM layout
>between an IN and OUT operations.
>
>* Why Linux Kernel Storage System needs Copy Offload support now ?
>-----------------------------------------------------------------------
>
>With the rise of the SNIA Computational Storage TWG and solutions [2],
>existing SCSI XCopy support in the protocol, recent advancement in the
>Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
>DMA support in the Linux Kernel mainly for NVMe devices [7] and
>eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
>from Copy offload operation.
>
>With this background we have significant number of use-cases which are
>strong candidates waiting for outstanding Linux Kernel Block Layer Copy
>Offload support, so that Linux Kernel Storage subsystem can to address
>previously mentioned problems [1] and allow efficient offloading of the
>data related operations. (Such as move/copy etc.)
>
>For reference following is the list of the use-cases/candidates waiting
>for Copy Offload support :-
>
>1. SCSI-attached storage arrays.
>2. Stacking drivers supporting XCopy DM/MD.
>3. Computational Storage solutions.
>7. File systems :- Local, NFS and Zonefs.
>4. Block devices :- Distributed, local, and Zoned devices.
>5. Peer to Peer DMA support solutions.
>6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
>
>* What we will discuss in the proposed session ?
>-----------------------------------------------------------------------
>
>I'd like to propose a session to go over this topic to understand :-
>
>1. What are the blockers for Copy Offload implementation ?
>2. Discussion about having a file system interface.
>3. Discussion about having right system call for user-space.
>4. What is the right way to move this work forward ?
>5. How can we help to contribute and move this work forward ?
>
>* Required Participants :-
>-----------------------------------------------------------------------
>
>I'd like to invite file system, block layer, and device drivers
>developers to:-
>
>1. Share their opinion on the topic.
>2. Share their experience and any other issues with [4].
>3. Uncover additional details that are missing from this proposal.
>
>Required attendees :-
>
>Martin K. Petersen
>Jens Axboe
>Christoph Hellwig
>Bart Van Assche
>Zach Brown
>Roland Dreier
>Ric Wheeler
>Trond Myklebust
>Mike Snitzer
>Keith Busch
>Sagi Grimberg
>Hannes Reinecke
>Frederick Knight
>Mikulas Patocka
>Keith Busch
>
>Regards,
>Chaitanya
>
>[1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
>[2] https://www.snia.org/computational
>https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
>      https://www.eideticom.com/products.html
>https://www.xilinx.com/applications/data-center/computational-storage.html
>[3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
>[4] https://www.spinics.net/lists/linux-block/msg00599.html
>[5] https://lwn.net/Articles/793585/
>[6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
>namespaces-zns-as-go-to-industry-technology/
>[7] https://github.com/sbates130272/linux-p2pmem
>[8] https://kernel.dk/io_uring.pdf


I would like to participate in this discussion too.

Cc'in Selva and Kanchan, who have been posting several series for NVMe
Simple Copy (SCC). Even though SCC is a very narrow use-case of
copy-offload, it seems like a good start to start getting generic code
in the block layer.

Javier


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Johannes Thumshirn]

On 11/05/2021 02:15, Chaitanya Kulkarni wrote:
> Hi,
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
> 
> * Problem :-
> -----------------------------------------------------------------------
> 
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
> 
> * Current state of the work :-
> -----------------------------------------------------------------------
> 
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
> 
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> -----------------------------------------------------------------------
> 
> With the rise of the SNIA Computational Storage TWG and solutions [2],
> existing SCSI XCopy support in the protocol, recent advancement in the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
> 
> With this background we have significant number of use-cases which are
> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
> Offload support, so that Linux Kernel Storage subsystem can to address
> previously mentioned problems [1] and allow efficient offloading of the
> data related operations. (Such as move/copy etc.)
> 
> For reference following is the list of the use-cases/candidates waiting
> for Copy Offload support :-
> 
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
> 
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> -----------------------------------------------------------------------
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
> 
> Required attendees :-
> 
> Martin K. Petersen
> Jens Axboe
> Christoph Hellwig
> Bart Van Assche
> Zach Brown
> Roland Dreier
> Ric Wheeler
> Trond Myklebust
> Mike Snitzer
> Keith Busch
> Sagi Grimberg
> Hannes Reinecke
> Frederick Knight
> Mikulas Patocka
> Keith Busch
>

I would like to participate in this discussion as well. A generic block layer
copy API is extremely helpful for filesystem garbage collection and copy operations
like copy_file_range().



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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Erwin van Londen]

[-- Attachment #1.1: Type: text/plain, Size: 5795 bytes --]



On Tue, 2021-05-11 at 00:15 +0000, Chaitanya Kulkarni wrote:
> Hi,
> 
> * Background :-
> ---------------------------------------------------------------------
> --
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the
> rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the
> common
> operation which is popular in the kernel and is not merged yet is
> Copy
> offload over the fabrics or on to the device.
> 
> * Problem :-
> ---------------------------------------------------------------------
> --
> 
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These
> two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular
> READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
> 
> * Current state of the work :-
> ---------------------------------------------------------------------
> --
> 
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a
> suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
> 
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> ---------------------------------------------------------------------
> --
> 
> With the rise of the SNIA Computational Storage TWG and solutions
> [2],
> existing SCSI XCopy support in the protocol, recent advancement in
> the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
> 
> With this background we have significant number of use-cases which
> are
> strong candidates waiting for outstanding Linux Kernel Block Layer
> Copy
> Offload support, so that Linux Kernel Storage subsystem can to
> address
> previously mentioned problems [1] and allow efficient offloading of
> the
> data related operations. (Such as move/copy etc.)
> 
> For reference following is the list of the use-cases/candidates
> waiting
> for Copy Offload support :-
> 
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
> 
> * What we will discuss in the proposed session ?
> ---------------------------------------------------------------------
> --
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> ---------------------------------------------------------------------
> --
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
> 
> Required attendees :-
> 
> Martin K. Petersen
> Jens Axboe
> Christoph Hellwig
> Bart Van Assche
> Zach Brown
> Roland Dreier
> Ric Wheeler
> Trond Myklebust
> Mike Snitzer
> Keith Busch
> Sagi Grimberg
> Hannes Reinecke
> Frederick Knight
> Mikulas Patocka
> Keith Busch
> 
> Regards,
> Chaitanya
> 

+1 here. I would like to see how this pans out as many differences may
be observed from a standards, implementation and operations point of
view.

> [1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
> [2] https://www.snia.org/computational
> https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
>       https://www.eideticom.com/products.html
> https://www.xilinx.com/applications/data-center/computational-storage.html
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
> [4] https://www.spinics.net/lists/linux-block/msg00599.html
> [5] https://lwn.net/Articles/793585/
> [6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
> namespaces-zns-as-go-to-industry-technology/
> [7] https://github.com/sbates130272/linux-p2pmem
> [8] https://kernel.dk/io_uring.pdf
> 
> 
> 
> 
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://listman.redhat.com/mailman/listinfo/dm-devel
> 

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Hannes Reinecke]

On 5/11/21 2:15 AM, Chaitanya Kulkarni wrote:
> Hi,
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
The neverending topic.

Count me in.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Himanshu Madhani]

> On May 10, 2021, at 7:15 PM, Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> wrote:
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.

I would like to participate in this discussion as well. 

--
Himanshu Madhani	 Oracle Linux Engineering


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Kanchan Joshi]

> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
>
> I'd like to propose a session to go over this topic to understand :-
>
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
>
> * Required Participants :-
> -----------------------------------------------------------------------
>
> I'd like to invite file system, block layer, and device drivers
> developers to:-
>
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
>
I'd like to participate in discussion.
Hopefully we can get consensus on some elements (or discover new
issues) before Dec.
An async-interface (via io_uring) would be good to be discussed while
we are at it.


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 5/10/21 5:15 PM, Chaitanya Kulkarni wrote:
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?

We need to achieve agreement about an approach. The text below is my
attempt at guiding the discussion. A HTML version is available at
https://github.com/bvanassche/linux-kernel-copy-offload. As usual,
feedback is welcome.

Bart.


# Implementing Copy Offloading in the Linux Kernel

## Introduction

Efforts to add copy offloading support in the Linux kernel started considerable
time ago. Despite this copy offloading support is not yet upstream and there is
no detailed plan yet of how to implement copy offloading.

This document outlines a possible implementation. The purpose of this document
is to help guiding the conversations around copy offloading.

## Block Layer

We need an interface to pass copy offload requests from user space or file
systems to block drivers. Although the first implementation of copy offloading
added a single operation to the block layer for copy offloading, there seems
to be agreement today to implement copy offloading as two operations,
namely `REQ_COPY_IN` and `REQ_COPY_OUT`.

A possible approach is as follows:

* Fall back to a non-offloaded copy operation if necessary, e.g. if copy
  offloading is not supported or if data is encrypted and the ciphertext
  depends on the LBA. The following code may be a good starting point:
  `drivers/md/dm-kcopyd.c`.
* If the block driver supports copy offloading, submit the `REQ_COPY_IN`
  operation first. The block driver stores the data ranges associated with the
  `REQ_COPY_IN` operation.
* Wait for completion of the `REQ_COPY_IN` operation.
* After the `REQ_COPY_IN` operation has completed, submit the `REQ_COPY_OUT`
  operation and include a reference to the `REQ_COPY_IN` operation. If the
  block driver that receives the `REQ_COPY_OUT` operation receives a matching
  `REQ_COPY_IN` operation, offload the copy operation. Otherwise report that no
  data has been copied and let the block layer perform a non-offloaded copy
  operation.

The operation type is stored in the top bits of the `bi_opf` member of struct
bio.  With each bio a single data buffer and a single contiguous byte range on
the storage medium are associated. Pointers to the data buffer occur in
`bi_io_vec[]`. The affected byte range is represented by `bi_iter.bi_sector` and
`bi_iter.bi_size`.

While the NVMe and SCSI copy offload commands both support multiple source
ranges, XCOPY supports multiple destination ranges while the NVMe simple copy
command supports a single destination range.

Possible approaches for passing the data ranges involved in a copy operation
from the block layer to block drivers are as follows:

* Attach a bio to each copy offload request and encode all relevant copy
  offload parameters in that data buffer. These parameters include source
  device and source ranges for `REQ_COPY_IN` and destination device and
  destination ranges for `REQ_COPY_OUT`. Let the block drivers translate these
  parameters into something the storage device understands (NVMe simple copy
  parameters or SCSI XCOPY parameters). Fill in the parameter structure size
  in `bi_iter.bi_size`. Set `bi_vcnt` to 1 and fill in `bio->bi_io_vec[0]`.
* Map each source range and each destination range onto a different bio. Link
  all the bios with the `bi_next` pointer and attach these bios to the copy
  offload requests. Leave `bi_vcnt` zero. This is related but not identical to
  the approach followed by `__blkdev_issue_discard()`.

I think that the first approach would require more changes in the device mapper
than the second approach since the device mapper code knows how to split bios
but not how to split a buffer with LBA range descriptors.

The following code needs to be modified no matter how copy offloading is
implemented:

* Request cloning. The code for checking the limits before request are cloned
  compares `blk_rq_sectors()` with `max_sectors`. This is inappropriate for
  `REQ_COPY_*` requests.
* Request splitting. `bio_split()` assumes that `bi_iter.bi_size` represents
  the number of bytes affected on the medium.
* Code related to retrying the original requests of a merged request with
  mixed failfast attributes, e.g. `blk_rq_err_bytes()`.
* Code related to partially completing a request, e.g. `blk_update_request()`.
* The code for merging block layer requests.
* `blk_mq_end_request()` since it calls `blk_update_request()` and
  `blk_rq_bytes()`.
* The plugging code because of the following test in the plugging code:
  `blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE`.
* The I/O accounting code (task_io_account_read()) since that code uses
  bio_has_data() and hence skips discard, secure erase and write zeroes
  requests:
```
static inline bool bio_has_data(struct bio *bio)
{
	return bio && bio->bi_iter.bi_size &&
	    bio_op(bio) != REQ_OP_DISCARD &&
	    bio_op(bio) != REQ_OP_SECURE_ERASE &&
	    bio_op(bio) != REQ_OP_WRITE_ZEROESy;
}
```

Block drivers will need to use the `special_vec` member of struct request to
pass the copy offload parameters to the storage device. That member is used
e.g. when a REQ_OP_DISCARD operation is submitted to an NVMe driver. The SCSI
sd driver uses `special_vec` while processing an UNMAP or WRITE SAME command.

## Device Mapper

The device mapper may have to split a request. As an example, LVM is
based on the dm-linear driver. A request that is submitted to an LVM volume
has to be split if it affects multiple block devices. Copy offload requests
that affect multiple block devices should be split or should be onloaded.

The call chain for bio-based dm drivers is as follows:
```
dm_submit_bio(bio)
-> __split_and_process_bio(md, map, bio)
  -> __split_and_process_non_flush(clone_info)
    -> __clone_and_map_data_bio(clone_info, target_info, sector, len)
      -> clone_bio(dm_target_io, bio, sector, len)
      -> __map_bio(dm_target_io)
        -> ti->type->map(dm_target_io, clone)
```

## NVMe

Process copy offload commands by translating REQ_COPY_OUT requests into simple
copy commands.

## SCSI

>From inside `sd_revalidate_disk()`, query the third-party copy VPD page. Extract
the following parameters (see also SPC-6):

* MAXIMUM CSCD DESCRIPTOR COUNT
* MAXIMUM SEGMENT DESCRIPTOR COUNT
* MAXIMUM DESCRIPTOR LIST LENGTH
* Supported third-party copy commands.
* SUPPORTED CSCD DESCRIPTOR ID (0 or more)
* ROD type descriptor (0 or more)
* TOTAL CONCURRENT COPIES
* MAXIMUM IDENTIFIED CONCURRENT COPIES
* MAXIMUM SEGMENT LENGTH

>From inside `sd_init_command()`, translate REQ_COPY_OUT into either EXTENDED
COPY or POPULATE TOKEN + WRITE USING TOKEN.

Set the parameters in the copy offload commands as follows:

* We may have to set the STR bit. From SPC-6: "A sequential striped (STR) bit
  set to one specifies to the copy manager that the majority of the block
  device references in the parameter list represent sequential access of
  several block devices that are striped. This may be used by the copy manager
  to perform reads from a copy source block device at any time and in any
  order during processing of an EXTENDED COPY command as described in
  6.6.5.3. A STR bit set to zero specifies to the copy manager that disk
  references, if any, may not be sequential."
* Set the LIST ID USAGE field to 3 and the LIST ID to 0. This means that
  neither "held data" nor the RECEIVE COPY STATUS command are supported. This
  improves security because the data that is being copied cannot be accessed
  via the LIST ID.
* We may have to set the G_SENSE (good with sense data) bit. From SPC-6: " If
  the G _SENSE bit is set to one and the copy manager completes the EXTENDED
  COPY command with GOOD status, then the copy manager shall include sense
  data with the GOOD status in which the sense key is set to COMPLETED, the
  additional sense code is set to EXTENDED COPY INFORMATION AVAILABLE, and the
  COMMAND-SPECIFIC INFORMATION field is set to the number of segment
  descriptors the copy manager has processed."
* Clear the IMMED bit.

## System Call Interface

To submit copy offload requests from user space, we need:

* A system call for passing these requests, e.g. copy_file_range() or io_uring.
* Add a copy offload parameter format description to the user space ABI. The
  parameters include source device, source ranges, destination device and
  destination ranges.
* A flag that indicates whether or not it is acceptable to fall back to
  onloading the copy operation.

## Sysfs Interface

To do: define which aspects of copy offloading should be configurable through
new sysfs parameters under /sys/block/*/queue/.

## See Also

* Martin Petersen, [Copy
  Offload](https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg28998.html),
  linux-scsi, 28 May 2014.
* Mikulas Patocka, [ANNOUNCE: SCSI XCOPY support for the kernel and device
  mapper](https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg686111.html),
  15 July 2014.
* [kcopyd documentation](https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/kcopyd.html), kernel.org.
* Martin K. Petersen, [Copy Offload - Here Be Dragons](http://mkp.net/pubs/xcopy.pdf), 2019-08-21.
* Martin K. Petersen, [Re: [dm-devel] [RFC PATCH v2 1/2] block: add simple copy
support](https://lore.kernel.org/linux-nvme/yq1blf3smcl.fsf@ca-mkp.ca.oracle.com/), linux-nvme mailing list, 2020-12-08.
* NVM Express Organization, [NVMe - TP 4065b Simple Copy Command 2021.01.25 -
  Ratified.pdf](https://workspace.nvmexpress.org/apps/org/workgroup/allmembers/download.php/4773/NVMe%20-%20TP%204065b%20Simple%20Copy%20Command%202021.01.25%20-%20Ratified.pdf), 2021-01-25.
* Selvakumar S, [[RFC PATCH v5 0/4] add simple copy
  support](https://lore.kernel.org/linux-nvme/20210219124517.79359-1-selvakuma.s1@samsung.com/),
  linux-nvme, 2021-02-19.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Chaitanya Kulkarni]

On 5/10/21 17:15, Chaitanya Kulkarni wrote:
> Hi,
>
> * Background :-
> -----------------------------------------------------------------------
>
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
>
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
>
> * Problem :-
> -----------------------------------------------------------------------
>
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
>
> * Current state of the work :-
> -----------------------------------------------------------------------
>
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
>
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> -----------------------------------------------------------------------
>
> With the rise of the SNIA Computational Storage TWG and solutions [2],
> existing SCSI XCopy support in the protocol, recent advancement in the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
>
> With this background we have significant number of use-cases which are
> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
> Offload support, so that Linux Kernel Storage subsystem can to address
> previously mentioned problems [1] and allow efficient offloading of the
> data related operations. (Such as move/copy etc.)
>
> For reference following is the list of the use-cases/candidates waiting
> for Copy Offload support :-
>
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
>
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
>
> I'd like to propose a session to go over this topic to understand :-
>
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
>
> * Required Participants :-
> -----------------------------------------------------------------------
>
> I'd like to invite file system, block layer, and device drivers
> developers to:-
>
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
>
> Required attendees :-
>
> Martin K. Petersen
> Jens Axboe
> Christoph Hellwig
> Bart Van Assche
> Zach Brown
> Roland Dreier
> Ric Wheeler
> Trond Myklebust
> Mike Snitzer
> Keith Busch
> Sagi Grimberg
> Hannes Reinecke
> Frederick Knight
> Mikulas Patocka
> Keith Busch
>
> Regards,
> Chaitanya
>
> [1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
> [2] https://www.snia.org/computational
> https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
>       https://www.eideticom.com/products.html
> https://www.xilinx.com/applications/data-center/computational-storage.html
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
> [4] https://www.spinics.net/lists/linux-block/msg00599.html
> [5] https://lwn.net/Articles/793585/
> [6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
> namespaces-zns-as-go-to-industry-technology/
> [7] https://github.com/sbates130272/linux-p2pmem
> [8] https://kernel.dk/io_uring.pdf
>
>

Mail server is dropping emails from the mailing list, adding personal
email address.





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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nikos Tsironis]

On 5/11/21 3:15 AM, Chaitanya Kulkarni wrote:
> Hi,
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
> 
> * Problem :-
> -----------------------------------------------------------------------
> 
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
> 
> * Current state of the work :-
> -----------------------------------------------------------------------
> 
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
> 
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> -----------------------------------------------------------------------
> 
> With the rise of the SNIA Computational Storage TWG and solutions [2],
> existing SCSI XCopy support in the protocol, recent advancement in the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
> 
> With this background we have significant number of use-cases which are
> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
> Offload support, so that Linux Kernel Storage subsystem can to address
> previously mentioned problems [1] and allow efficient offloading of the
> data related operations. (Such as move/copy etc.)
> 
> For reference following is the list of the use-cases/candidates waiting
> for Copy Offload support :-
> 
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
> 
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> -----------------------------------------------------------------------
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
> 
> Required attendees :-
> 
> Martin K. Petersen
> Jens Axboe
> Christoph Hellwig
> Bart Van Assche
> Zach Brown
> Roland Dreier
> Ric Wheeler
> Trond Myklebust
> Mike Snitzer
> Keith Busch
> Sagi Grimberg
> Hannes Reinecke
> Frederick Knight
> Mikulas Patocka
> Keith Busch
> 
> Regards,
> Chaitanya
> 
> [1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
> [2] https://www.snia.org/computational
> https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
>        https://www.eideticom.com/products.html
> https://www.xilinx.com/applications/data-center/computational-storage.html
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
> [4] https://www.spinics.net/lists/linux-block/msg00599.html
> [5] https://lwn.net/Articles/793585/
> [6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
> namespaces-zns-as-go-to-industry-technology/
> [7] https://github.com/sbates130272/linux-p2pmem
> [8] https://kernel.dk/io_uring.pdf
> 

I would like to participate in this discussion too.

Thanks,
Nikos

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 12.05.2021 07:30, Johannes Thumshirn wrote:
>On 11/05/2021 02:15, Chaitanya Kulkarni wrote:
>> Hi,
>>
>> * Background :-
>> -----------------------------------------------------------------------
>>
>> Copy offload is a feature that allows file-systems or storage devices
>> to be instructed to copy files/logical blocks without requiring
>> involvement of the local CPU.
>>
>> With reference to the RISC-V summit keynote [1] single threaded
>> performance is limiting due to Denard scaling and multi-threaded
>> performance is slowing down due Moore's law limitations. With the rise
>> of SNIA Computation Technical Storage Working Group (TWG) [2],
>> offloading computations to the device or over the fabrics is becoming
>> popular as there are several solutions available [2]. One of the common
>> operation which is popular in the kernel and is not merged yet is Copy
>> offload over the fabrics or on to the device.
>>
>> * Problem :-
>> -----------------------------------------------------------------------
>>
>> The original work which is done by Martin is present here [3]. The
>> latest work which is posted by Mikulas [4] is not merged yet. These two
>> approaches are totally different from each other. Several storage
>> vendors discourage mixing copy offload requests with regular READ/WRITE
>> I/O. Also, the fact that the operation fails if a copy request ever
>> needs to be split as it traverses the stack it has the unfortunate
>> side-effect of preventing copy offload from working in pretty much
>> every common deployment configuration out there.
>>
>> * Current state of the work :-
>> -----------------------------------------------------------------------
>>
>> With [3] being hard to handle arbitrary DM/MD stacking without
>> splitting the command in two, one for copying IN and one for copying
>> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
>> candidate. Also, with [4] there is an unresolved problem with the
>> two-command approach about how to handle changes to the DM layout
>> between an IN and OUT operations.
>>
>> * Why Linux Kernel Storage System needs Copy Offload support now ?
>> -----------------------------------------------------------------------
>>
>> With the rise of the SNIA Computational Storage TWG and solutions [2],
>> existing SCSI XCopy support in the protocol, recent advancement in the
>> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
>> DMA support in the Linux Kernel mainly for NVMe devices [7] and
>> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
>> from Copy offload operation.
>>
>> With this background we have significant number of use-cases which are
>> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
>> Offload support, so that Linux Kernel Storage subsystem can to address
>> previously mentioned problems [1] and allow efficient offloading of the
>> data related operations. (Such as move/copy etc.)
>>
>> For reference following is the list of the use-cases/candidates waiting
>> for Copy Offload support :-
>>
>> 1. SCSI-attached storage arrays.
>> 2. Stacking drivers supporting XCopy DM/MD.
>> 3. Computational Storage solutions.
>> 7. File systems :- Local, NFS and Zonefs.
>> 4. Block devices :- Distributed, local, and Zoned devices.
>> 5. Peer to Peer DMA support solutions.
>> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
>>
>> * What we will discuss in the proposed session ?
>> -----------------------------------------------------------------------
>>
>> I'd like to propose a session to go over this topic to understand :-
>>
>> 1. What are the blockers for Copy Offload implementation ?
>> 2. Discussion about having a file system interface.
>> 3. Discussion about having right system call for user-space.
>> 4. What is the right way to move this work forward ?
>> 5. How can we help to contribute and move this work forward ?
>>
>> * Required Participants :-
>> -----------------------------------------------------------------------
>>
>> I'd like to invite file system, block layer, and device drivers
>> developers to:-
>>
>> 1. Share their opinion on the topic.
>> 2. Share their experience and any other issues with [4].
>> 3. Uncover additional details that are missing from this proposal.
>>
>> Required attendees :-
>>
>> Martin K. Petersen
>> Jens Axboe
>> Christoph Hellwig
>> Bart Van Assche
>> Zach Brown
>> Roland Dreier
>> Ric Wheeler
>> Trond Myklebust
>> Mike Snitzer
>> Keith Busch
>> Sagi Grimberg
>> Hannes Reinecke
>> Frederick Knight
>> Mikulas Patocka
>> Keith Busch
>>
>
>I would like to participate in this discussion as well. A generic block layer
>copy API is extremely helpful for filesystem garbage collection and copy operations
>like copy_file_range().


Hi all,

Since we are not going to be able to talk about this at LSF/MM, a few of
us thought about holding a dedicated virtual discussion about Copy
Offload. I believe we can use Chaitanya's thread as a start. Given the
current state of the current patches, I would propose that we focus on
the next step to get the minimal patchset that can go upstream so that
we can build from there.

Before we try to find a date and a time that fits most of us, who would
be interested in participating?

Thanks,
Javier

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Johannes Thumshirn]

On 28/09/2021 21:13, Javier González wrote:
> Since we are not going to be able to talk about this at LSF/MM, a few of
> us thought about holding a dedicated virtual discussion about Copy
> Offload. I believe we can use Chaitanya's thread as a start. Given the
> current state of the current patches, I would propose that we focus on
> the next step to get the minimal patchset that can go upstream so that
> we can build from there.
> 
> Before we try to find a date and a time that fits most of us, who would
> be interested in participating?

I'd definitively be interested in participating.



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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Chaitanya Kulkarni]

Javier,

> 
> Hi all,
> 
> Since we are not going to be able to talk about this at LSF/MM, a few of
> us thought about holding a dedicated virtual discussion about Copy
> Offload. I believe we can use Chaitanya's thread as a start. Given the
> current state of the current patches, I would propose that we focus on
> the next step to get the minimal patchset that can go upstream so that
> we can build from there.
> 

I agree with having a call as it has been two years I'm trying to have 
this discussion.

Before we setup a call, please summarize following here :-

1. Exactly what work has been done so far.
2. What kind of feedback you got.
3. What are the exact blockers/objections.
4. Potential ways of moving forward.

Although this all information is present in the mailing archives it is 
scattered all over the places, looking at the long CC list above we need 
to get the everyone on the same page in order to have a productive call.

Once we have above discussion we can setup a precise agenda and assign 
slots.

> Before we try to find a date and a time that fits most of us, who would
> be interested in participating?
> 
> Thanks,
> Javier

-ck

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 30.09.2021 09:43, Chaitanya Kulkarni wrote:
>Javier,
>
>>
>> Hi all,
>>
>> Since we are not going to be able to talk about this at LSF/MM, a few of
>> us thought about holding a dedicated virtual discussion about Copy
>> Offload. I believe we can use Chaitanya's thread as a start. Given the
>> current state of the current patches, I would propose that we focus on
>> the next step to get the minimal patchset that can go upstream so that
>> we can build from there.
>>
>
>I agree with having a call as it has been two years I'm trying to have
>this discussion.
>
>Before we setup a call, please summarize following here :-
>
>1. Exactly what work has been done so far.
>2. What kind of feedback you got.
>3. What are the exact blockers/objections.
>4. Potential ways of moving forward.
>
>Although this all information is present in the mailing archives it is
>scattered all over the places, looking at the long CC list above we need
>to get the everyone on the same page in order to have a productive call.
>
>Once we have above discussion we can setup a precise agenda and assign
>slots.

Sounds reasonable. Let me collect all this information and post it here.
I will maintain a list of people that has showed interest on joining.
For now:

   - Martin
   - Johannes
   - Fred
   - Chaitanya
   - Adam
   - Kanchan
   - Selva
   - Nitesh
   - Javier

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 9/28/21 12:13 PM, Javier González wrote:
> Since we are not going to be able to talk about this at LSF/MM, a few of
> us thought about holding a dedicated virtual discussion about Copy
> Offload. I believe we can use Chaitanya's thread as a start. Given the
> current state of the current patches, I would propose that we focus on
> the next step to get the minimal patchset that can go upstream so that
> we can build from there.
> 
> Before we try to find a date and a time that fits most of us, who would
> be interested in participating?

Given the technical complexity of this topic and also that the people who are
interested live in multiple time zones, I prefer email to discuss the technical
aspects of this work. My attempt to summarize how to implement copy offloading
is available here: https://github.com/bvanassche/linux-kernel-copy-offload.
Feedback on this text is welcome.

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 30.09.2021 09:43, Chaitanya Kulkarni wrote:
>Javier,
>
>>
>> Hi all,
>>
>> Since we are not going to be able to talk about this at LSF/MM, a few of
>> us thought about holding a dedicated virtual discussion about Copy
>> Offload. I believe we can use Chaitanya's thread as a start. Given the
>> current state of the current patches, I would propose that we focus on
>> the next step to get the minimal patchset that can go upstream so that
>> we can build from there.
>>
>
>I agree with having a call as it has been two years I'm trying to have
>this discussion.
>
>Before we setup a call, please summarize following here :-
>
>1. Exactly what work has been done so far.


We can categorize that into two sets. First one for XCopy (2014), and
second one for NVMe Copy (2021).

XCOPY set *********
- block-generic copy command (single range, between one
   source/destination device)
- ioctl interface for the above
- SCSI plumbing (block-generic to XCOPY conversion)
- device-mapper support: offload copy whenever possible (if IO is not
   split while traveling layers of virtual devices)

NVMe-Copy set *************
- block-generic copy command (multiple ranges, between one
   source/destination device)
- ioctl interface for the above
- NVMe plumbing (block-generic to NVMe Copy conversion)
- copy-emulation (read + write) in block-layer
- device-mapper support: no offload, rather fall back to copy-emulation


>2. What kind of feedback you got.

For NVMe Copy, the major points are - a) add copy-emulation in
block-layer and use that if copy-offload is not natively supported by
device b) user-interface (ioctl) should be extendable for copy across
two devices (one source, one destination) c) device-mapper targets
should support copy-offload, whenever possible

"whenever possible" cases get reduced compared to XCOPY because NVMe
Copy is wit

>3. What are the exact blockers/objections.

I think it was device-mapper for XCOPY and remains the same for NVMe
Copy as well.  Device-mapper support requires decomposing copy operation
to read and write.  While that is not great for efficiency PoV, bigger
concern is to check if we are taking the same route as XCOPY.

 From Martin's document (http://mkp.net/pubs/xcopy.pdf), if I got it
right, one the major blocker is having more failure cases than
successful ones. And that did not justify the effort/code to wire up
device mapper.  Is that a factor to consider for NVMe Copy (which is
narrower in scope than XCOPY).

>4. Potential ways of moving forward.

a) we defer attempt device-mapper support (until NVMe has
support/usecase), and address everything else (reusable user-interface
etc.)

b) we attempt device-mapper support (by moving to composite read+write
communication between block-layer and nvme)


Is this enough in your mind to move forward with a specific agenda? If
we can, I would like to target the meetup in the next 2 weeks.

Thanks,
Javier

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 30.09.2021 09:20, Bart Van Assche wrote:
>On 9/28/21 12:13 PM, Javier González wrote:
>>Since we are not going to be able to talk about this at LSF/MM, a few of
>>us thought about holding a dedicated virtual discussion about Copy
>>Offload. I believe we can use Chaitanya's thread as a start. Given the
>>current state of the current patches, I would propose that we focus on
>>the next step to get the minimal patchset that can go upstream so that
>>we can build from there.
>>
>>Before we try to find a date and a time that fits most of us, who would
>>be interested in participating?
>
>Given the technical complexity of this topic and also that the people who are
>interested live in multiple time zones, I prefer email to discuss the technical
>aspects of this work. My attempt to summarize how to implement copy offloading
>is available here: https://protect2.fireeye.com/v1/url?k=ba7e5d9a-e5e564d5-ba7fd6d5-0cc47a30d446-07a47f3f53cbfe53&q=1&e=c3973bdc-b6fd-43fb-80e6-0c86cb6b4d5f&u=https%3A%2F%2Fgithub.com%2Fbvanassche%2Flinux-kernel-copy-offload.
>Feedback on this text is welcome.

Thanks for sharing this Bart.

I agree that the topic is complex. However, we have not been able to
find a clear path forward in the mailing list.

What do you think about joining the call to talk very specific next
steps to get a patchset that we can start reviewing in detail.

I think that your presence in the call will help us all.

What do you think?


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 10/6/21 3:05 AM, Javier González wrote:
> I agree that the topic is complex. However, we have not been able to
> find a clear path forward in the mailing list.

Hmm ... really? At least Martin Petersen and I consider device mapper 
support essential. How about starting from Mikulas' patch series that 
supports the device mapper? See also 
https://lore.kernel.org/all/alpine.LRH.2.02.2108171630120.30363@file01.intranet.prod.int.rdu2.redhat.com/

> What do you think about joining the call to talk very specific next
> steps to get a patchset that we can start reviewing in detail.

I can do that.

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

Chaitanya,

Did you have a chance to look at the answers below?

I would like to start finding candidate dates throughout the next couple
of weeks.

Thanks,
Javier

On 06.10.2021 12:01, Javier González wrote:
>On 30.09.2021 09:43, Chaitanya Kulkarni wrote:
>>Javier,
>>
>>>
>>>Hi all,
>>>
>>>Since we are not going to be able to talk about this at LSF/MM, a few of
>>>us thought about holding a dedicated virtual discussion about Copy
>>>Offload. I believe we can use Chaitanya's thread as a start. Given the
>>>current state of the current patches, I would propose that we focus on
>>>the next step to get the minimal patchset that can go upstream so that
>>>we can build from there.
>>>
>>
>>I agree with having a call as it has been two years I'm trying to have
>>this discussion.
>>
>>Before we setup a call, please summarize following here :-
>>
>>1. Exactly what work has been done so far.
>
>
>We can categorize that into two sets. First one for XCopy (2014), and
>second one for NVMe Copy (2021).
>
>XCOPY set *********
>- block-generic copy command (single range, between one
>  source/destination device)
>- ioctl interface for the above
>- SCSI plumbing (block-generic to XCOPY conversion)
>- device-mapper support: offload copy whenever possible (if IO is not
>  split while traveling layers of virtual devices)
>
>NVMe-Copy set *************
>- block-generic copy command (multiple ranges, between one
>  source/destination device)
>- ioctl interface for the above
>- NVMe plumbing (block-generic to NVMe Copy conversion)
>- copy-emulation (read + write) in block-layer
>- device-mapper support: no offload, rather fall back to copy-emulation
>
>
>>2. What kind of feedback you got.
>
>For NVMe Copy, the major points are - a) add copy-emulation in
>block-layer and use that if copy-offload is not natively supported by
>device b) user-interface (ioctl) should be extendable for copy across
>two devices (one source, one destination) c) device-mapper targets
>should support copy-offload, whenever possible
>
>"whenever possible" cases get reduced compared to XCOPY because NVMe
>Copy is wit
>
>>3. What are the exact blockers/objections.
>
>I think it was device-mapper for XCOPY and remains the same for NVMe
>Copy as well.  Device-mapper support requires decomposing copy operation
>to read and write.  While that is not great for efficiency PoV, bigger
>concern is to check if we are taking the same route as XCOPY.
>
>From Martin's document (http://mkp.net/pubs/xcopy.pdf), if I got it
>right, one the major blocker is having more failure cases than
>successful ones. And that did not justify the effort/code to wire up
>device mapper.  Is that a factor to consider for NVMe Copy (which is
>narrower in scope than XCOPY).
>
>>4. Potential ways of moving forward.
>
>a) we defer attempt device-mapper support (until NVMe has
>support/usecase), and address everything else (reusable user-interface
>etc.)
>
>b) we attempt device-mapper support (by moving to composite read+write
>communication between block-layer and nvme)
>
>
>Is this enough in your mind to move forward with a specific agenda? If
>we can, I would like to target the meetup in the next 2 weeks.
>
>Thanks,
>Javier


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Chaitanya Kulkarni]

On 10/7/21 11:49 PM, Javier González wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 06.10.2021 10:33, Bart Van Assche wrote:
>> On 10/6/21 3:05 AM, Javier González wrote:
>>> I agree that the topic is complex. However, we have not been able to
>>> find a clear path forward in the mailing list.
>>
>> Hmm ... really? At least Martin Petersen and I consider device mapper
>> support essential. How about starting from Mikulas' patch series that
>> supports the device mapper? See also 
>> https://lore.kernel.org/all/alpine.LRH.2.02.2108171630120.30363@file01.intranet.prod.int.rdu2.redhat.com/ 
>>

When we add a new REQ_OP_XXX we need to make sure it will work with 
device mapper, so I agree with Bart and Martin.

Starting with Mikulas patches is a right direction as of now..

> 
> Thanks for the pointers. We are looking into Mikulas' patch - I agree
> that it is a good start.
> 
>>> What do you think about joining the call to talk very specific next
>>> steps to get a patchset that we can start reviewing in detail.
>>
>> I can do that.
> 
> Thanks. I will wait until Chaitanya's reply on his questions. We will
> start suggesting some dates then.
> 

I think at this point we need to at least decide on having a first call
focused on how to proceed forward with Mikulas approach  ...

Javier, can you please organize a call with people you listed in this 
thread earlier ?

> Thanks,
> Javier


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Hannes Reinecke]

On 10/29/21 2:21 AM, Chaitanya Kulkarni wrote:
> On 10/7/21 11:49 PM, Javier González wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 06.10.2021 10:33, Bart Van Assche wrote:
>>> On 10/6/21 3:05 AM, Javier González wrote:
>>>> I agree that the topic is complex. However, we have not been able to
>>>> find a clear path forward in the mailing list.
>>>
>>> Hmm ... really? At least Martin Petersen and I consider device mapper
>>> support essential. How about starting from Mikulas' patch series that
>>> supports the device mapper? See also
>>> https://lore.kernel.org/all/alpine.LRH.2.02.2108171630120.30363@file01.intranet.prod.int.rdu2.redhat.com/
>>>
> 
> When we add a new REQ_OP_XXX we need to make sure it will work with
> device mapper, so I agree with Bart and Martin.
> 
> Starting with Mikulas patches is a right direction as of now..
> 
>>
>> Thanks for the pointers. We are looking into Mikulas' patch - I agree
>> that it is a good start.
>>
>>>> What do you think about joining the call to talk very specific next
>>>> steps to get a patchset that we can start reviewing in detail.
>>>
>>> I can do that.
>>
>> Thanks. I will wait until Chaitanya's reply on his questions. We will
>> start suggesting some dates then.
>>
> 
> I think at this point we need to at least decide on having a first call
> focused on how to proceed forward with Mikulas approach  ...
> 
> Javier, can you please organize a call with people you listed in this
> thread earlier ?
> 
Also Keith presented his work on a simple zone-based remapping block 
device, which included an in-kernel copy offload facility.
Idea is to lift that as a standalone patch such that we can use it a 
fallback (ie software) implementation if no other copy offload mechanism 
is available.

Cheers,

Hannes
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hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 29.10.2021 00:21, Chaitanya Kulkarni wrote:
>On 10/7/21 11:49 PM, Javier González wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 06.10.2021 10:33, Bart Van Assche wrote:
>>> On 10/6/21 3:05 AM, Javier González wrote:
>>>> I agree that the topic is complex. However, we have not been able to
>>>> find a clear path forward in the mailing list.
>>>
>>> Hmm ... really? At least Martin Petersen and I consider device mapper
>>> support essential. How about starting from Mikulas' patch series that
>>> supports the device mapper? See also
>>> https://lore.kernel.org/all/alpine.LRH.2.02.2108171630120.30363@file01.intranet.prod.int.rdu2.redhat.com/
>>>
>
>When we add a new REQ_OP_XXX we need to make sure it will work with
>device mapper, so I agree with Bart and Martin.
>
>Starting with Mikulas patches is a right direction as of now..
>
>>
>> Thanks for the pointers. We are looking into Mikulas' patch - I agree
>> that it is a good start.
>>
>>>> What do you think about joining the call to talk very specific next
>>>> steps to get a patchset that we can start reviewing in detail.
>>>
>>> I can do that.
>>
>> Thanks. I will wait until Chaitanya's reply on his questions. We will
>> start suggesting some dates then.
>>
>
>I think at this point we need to at least decide on having a first call
>focused on how to proceed forward with Mikulas approach  ...
>
>Javier, can you please organize a call with people you listed in this
>thread earlier ?

Here you have a Doogle for end of next week and the week after OCP.
Please fill it out until Wednesday. I will set up a call with the
selected slot:

     https://doodle.com/poll/r2c8duy3r8g88v8q?utm_source=poll&utm_medium=link

Thanks,
Javier

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 29.10.2021 07:51, Hannes Reinecke wrote:
>On 10/29/21 2:21 AM, Chaitanya Kulkarni wrote:
>>On 10/7/21 11:49 PM, Javier González wrote:
>>>External email: Use caution opening links or attachments
>>>
>>>
>>>On 06.10.2021 10:33, Bart Van Assche wrote:
>>>>On 10/6/21 3:05 AM, Javier González wrote:
>>>>>I agree that the topic is complex. However, we have not been able to
>>>>>find a clear path forward in the mailing list.
>>>>
>>>>Hmm ... really? At least Martin Petersen and I consider device mapper
>>>>support essential. How about starting from Mikulas' patch series that
>>>>supports the device mapper? See also
>>>>https://lore.kernel.org/all/alpine.LRH.2.02.2108171630120.30363@file01.intranet.prod.int.rdu2.redhat.com/
>>>>
>>
>>When we add a new REQ_OP_XXX we need to make sure it will work with
>>device mapper, so I agree with Bart and Martin.
>>
>>Starting with Mikulas patches is a right direction as of now..
>>
>>>
>>>Thanks for the pointers. We are looking into Mikulas' patch - I agree
>>>that it is a good start.
>>>
>>>>>What do you think about joining the call to talk very specific next
>>>>>steps to get a patchset that we can start reviewing in detail.
>>>>
>>>>I can do that.
>>>
>>>Thanks. I will wait until Chaitanya's reply on his questions. We will
>>>start suggesting some dates then.
>>>
>>
>>I think at this point we need to at least decide on having a first call
>>focused on how to proceed forward with Mikulas approach  ...
>>
>>Javier, can you please organize a call with people you listed in this
>>thread earlier ?
>>
>Also Keith presented his work on a simple zone-based remapping block 
>device, which included an in-kernel copy offload facility.
>Idea is to lift that as a standalone patch such that we can use it a 
>fallback (ie software) implementation if no other copy offload 
>mechanism is available.
>

I believe this is in essence what we are trying to convey here: a
minimal patchset that enables Simple Copy and the infra around to extend
copy-offload use-cases.

I look forward to hear Keith's ideas around this!

Javier

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 10/28/21 10:51 PM, Hannes Reinecke wrote:
> Also Keith presented his work on a simple zone-based remapping block device, which included an in-kernel copy offload facility.
> Idea is to lift that as a standalone patch such that we can use it a fallback (ie software) implementation if no other copy offload mechanism is available.

Is a link to the presentation available?

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Keith Busch]

On Fri, Oct 29, 2021 at 09:15:43AM -0700, Bart Van Assche wrote:
> On 10/28/21 10:51 PM, Hannes Reinecke wrote:
> > Also Keith presented his work on a simple zone-based remapping block device, which included an in-kernel copy offload facility.
> > Idea is to lift that as a standalone patch such that we can use it a fallback (ie software) implementation if no other copy offload mechanism is available.
> 
> Is a link to the presentation available?

Thanks for the interest.

I didn't post them online as the conference didn't provide it, and I
don't think the slides would be particularly interesting without the
prepared speech anyway.

The presentation described a simple prototype implementing a redirection
table on zone block devices. There was one bullet point explaining how a
generic kernel implementation would be an improvement. For zoned block
devices, an "append" like copy offload would be an even better option.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Javier González]

On 29.10.2021 10:14, Javier González wrote:
>On 29.10.2021 00:21, Chaitanya Kulkarni wrote:
>>On 10/7/21 11:49 PM, Javier González wrote:
>>>External email: Use caution opening links or attachments
>>>
>>>
>>>On 06.10.2021 10:33, Bart Van Assche wrote:
>>>>On 10/6/21 3:05 AM, Javier González wrote:
>>>>>I agree that the topic is complex. However, we have not been able to
>>>>>find a clear path forward in the mailing list.
>>>>
>>>>Hmm ... really? At least Martin Petersen and I consider device mapper
>>>>support essential. How about starting from Mikulas' patch series that
>>>>supports the device mapper? See also
>>>>https://lore.kernel.org/all/alpine.LRH.2.02.2108171630120.30363@file01.intranet.prod.int.rdu2.redhat.com/
>>>>
>>
>>When we add a new REQ_OP_XXX we need to make sure it will work with
>>device mapper, so I agree with Bart and Martin.
>>
>>Starting with Mikulas patches is a right direction as of now..
>>
>>>
>>>Thanks for the pointers. We are looking into Mikulas' patch - I agree
>>>that it is a good start.
>>>
>>>>>What do you think about joining the call to talk very specific next
>>>>>steps to get a patchset that we can start reviewing in detail.
>>>>
>>>>I can do that.
>>>
>>>Thanks. I will wait until Chaitanya's reply on his questions. We will
>>>start suggesting some dates then.
>>>
>>
>>I think at this point we need to at least decide on having a first call
>>focused on how to proceed forward with Mikulas approach  ...
>>
>>Javier, can you please organize a call with people you listed in this
>>thread earlier ?
>
>Here you have a Doogle for end of next week and the week after OCP.
>Please fill it out until Wednesday. I will set up a call with the
>selected slot:
>
>    https://doodle.com/poll/r2c8duy3r8g88v8q?utm_source=poll&utm_medium=link
>
>Thanks,
>Javier

I sent the invite for the people that signed up into the Doodle. The
call will take place on Monday November 15th, 17.00-19.00 CET. See the
list of current participants below. If anyone else wants to participate,
please send me a note and I will extend the invite.

   Johannes.Thumshirn@wdc.com
   Vincent.fu@samsung.com
   a.dawn@samsung.com
   a.manzanares@samsung.com
   bvanassche@acm.org
   himanshu.madhani@oracle.com
   joshi.k@samsung.com
   kch@nvidia.com
   martin.petersen@oracle.com
   nj.shetty@samsung.com
   selvakuma.s1@samsung

Javier

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 11/16/21 05:43, Javier González wrote:
>              - Here, we need copy emulation to support encryption 
> without dealing with HW issues and garbage

Hi Javier,

Thanks very much for having taken notes and also for having shared 
these. Regarding the above comment, after the meeting I learned that the 
above is not correct. Encryption in Android is LBA independent and hence 
it should be possible to offload F2FS garbage collection in Android once 
the (UFS) storage controller supports this.

For the general case, I propose to let the dm-crypt driver decide 
whether or not to offload data copying since that driver knows whether 
or not data copying can be offloaded.

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 11/17/21 04:53, Javier González wrote:
> Thanks for sharing this. We will make sure that DM / MD are supported
> and then we can cover examples. Hopefully, you guys can help with the
> bits for dm-crypt to make the decision to offload when it make sense.

Will ask around to learn who should work on this.

> I will update the notes to keep them alive. Maybe we can have them open
> in your github page?

Feel free to submit a pull request.

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 11/19/21 02:47, Kanchan Joshi wrote:
> Given the multitude of things accumulated on this topic, Martin
> suggested to have a table/matrix.
> Some of those should go in the initial patchset, and the remaining are
> to be staged for subsequent work.
> Here is the attempt to split the stuff into two buckets. Please change
> if something needs to be changed below.
> 
> 1. Driver
> *********
> Initial: NVMe Copy command (single NS)
> Subsequent: Multi NS copy, XCopy/Token-based Copy
> 
> 2. Block layer
> **************
> Initial:
> - Block-generic copy (REQ_OP_COPY), with interface accommodating two block-devs
> - Emulation, when offload is natively absent
> - DM support (at least dm-linear)
> 
> 3. User-interface
> *****************
> Initial: new ioctl or io_uring opcode
> 
> 4. In-kernel user
> ******************
> Initial: at least one user
> - dm-kcopyd user (e.g. dm-clone), or FS requiring GC (F2FS/Btrfs)
> 
> Subsequent:
> - copy_file_range

Integrity support and inline encryption support are missing from the above
overview. Both are supported by the block layer. See also block/blk-integrity.c
and include/linux/blk-crypto.h. I'm not claiming that these should be supported
in the first version but I think it would be good to add these to the above
overview.

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nikos Tsironis]

On 3/9/22 10:51, Mikulas Patocka wrote:
> 
> Hi
> 
> Note that you must submit kcopyd callbacks from a single thread, otherwise
> there's a race condition in snapshot.
> 

Hi,

Thanks for the feedback. Yes, I'm aware of that.

> The snapshot code doesn't take locks in the copy_callback and it expects
> that the callbacks are serialized.
> 
> Maybe, adding the locks to copy_callback would solve it.
> 

That's what I did. I used a lock to ensure that kcopyd callbacks are
serialized for persistent snapshots.

For transient snapshots we can lift this limitation, and complete
pending exceptions out-of-oder and in "parallel", i.e., without
explicitly serializing kcopyd callbacks. The locks in pending_complete()
are enough in this case.

Nikos

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Mikulas Patocka]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 2404 bytes --]



On Tue, 8 Mar 2022, Nikos Tsironis wrote:

> My work focuses mainly on improving the IOPs and latency of the
> dm-snapshot target, in order to bring the performance of short-lived
> snapshots as close as possible to bare-metal performance.
> 
> My initial performance evaluation of dm-snapshot had revealed a big
> performance drop, while the snapshot is active; a drop which is not
> justified by COW alone.
> 
> Using fio with blktrace I had noticed that the per-CPU I/O distribution
> was uneven. Although many threads were doing I/O, only a couple of the
> CPUs ended up submitting I/O requests to the underlying device.
> 
> The same issue also affects dm-clone, when doing I/O with sizes smaller
> than the target's region size, where kcopyd is used for COW.
> 
> The bottleneck here is kcopyd serializing all I/O. Users of kcopyd, such
> as dm-snapshot and dm-clone, cannot take advantage of the increased I/O
> parallelism that comes with using blk-mq in modern multi-core systems,
> because I/Os are issued only by a single CPU at a time, the one on which
> kcopyd’s thread happens to be running.
> 
> So, I experimented redesigning kcopyd to prevent I/O serialization by
> respecting thread locality for I/Os and their completions. This made the
> distribution of I/O processing uniform across CPUs.
> 
> My measurements had shown that scaling kcopyd, in combination with
> scaling dm-snapshot itself [1] [2], can lead to an eventual performance
> improvement of ~300% increase in sustained throughput and ~80% decrease
> in I/O latency for transient snapshots, over the null_blk device.
> 
> The work for scaling dm-snapshot has been merged [1], but,
> unfortunately, I haven't been able to send upstream my work on kcopyd
> yet, because I have been really busy with other things the last couple
> of years.
> 
> I haven't looked into the details of copy offload yet, but it would be
> really interesting to see how it affects the performance of random and
> sequential workloads, and to check how, and if, scaling kcopyd affects
> the performance, in combination with copy offload.
> 
> Nikos

Hi

Note that you must submit kcopyd callbacks from a single thread, otherwise 
there's a race condition in snapshot.

The snapshot code doesn't take locks in the copy_callback and it expects 
that the callbacks are serialized.

Maybe, adding the locks to copy_callback would solve it.

Mikulas

[-- Attachment #2: Type: text/plain, Size: 98 bytes --]

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nikos Tsironis]

On 3/1/22 23:32, Chaitanya Kulkarni wrote:
> Nikos,
> 
>>> [8] https://kernel.dk/io_uring.pdf
>>
>> I would like to participate in the discussion too.
>>
>> The dm-clone target would also benefit from copy offload, as it heavily
>> employs dm-kcopyd. I have been exploring redesigning kcopyd in order to
>> achieve increased IOPS in dm-clone and dm-snapshot for small copies over
>> NVMe devices, but copy offload sounds even more promising, especially
>> for larger copies happening in the background (as is the case with
>> dm-clone's background hydration).
>>
>> Thanks,
>> Nikos
> 
> If you can document your findings here it will be great for me to
> add it to the agenda.
> 

My work focuses mainly on improving the IOPs and latency of the
dm-snapshot target, in order to bring the performance of short-lived
snapshots as close as possible to bare-metal performance.

My initial performance evaluation of dm-snapshot had revealed a big
performance drop, while the snapshot is active; a drop which is not
justified by COW alone.

Using fio with blktrace I had noticed that the per-CPU I/O distribution
was uneven. Although many threads were doing I/O, only a couple of the
CPUs ended up submitting I/O requests to the underlying device.

The same issue also affects dm-clone, when doing I/O with sizes smaller
than the target's region size, where kcopyd is used for COW.

The bottleneck here is kcopyd serializing all I/O. Users of kcopyd, such
as dm-snapshot and dm-clone, cannot take advantage of the increased I/O
parallelism that comes with using blk-mq in modern multi-core systems,
because I/Os are issued only by a single CPU at a time, the one on which
kcopyd’s thread happens to be running.

So, I experimented redesigning kcopyd to prevent I/O serialization by
respecting thread locality for I/Os and their completions. This made the
distribution of I/O processing uniform across CPUs.

My measurements had shown that scaling kcopyd, in combination with
scaling dm-snapshot itself [1] [2], can lead to an eventual performance
improvement of ~300% increase in sustained throughput and ~80% decrease
in I/O latency for transient snapshots, over the null_blk device.

The work for scaling dm-snapshot has been merged [1], but,
unfortunately, I haven't been able to send upstream my work on kcopyd
yet, because I have been really busy with other things the last couple
of years.

I haven't looked into the details of copy offload yet, but it would be
really interesting to see how it affects the performance of random and
sequential workloads, and to check how, and if, scaling kcopyd affects
the performance, in combination with copy offload.

Nikos

[1] https://lore.kernel.org/dm-devel/20190317122258.21760-1-ntsironis@arrikto.com/
[2] https://lore.kernel.org/dm-devel/425d7efe-ab3f-67be-264e-9c3b6db229bc@arrikto.com/

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nikos Tsironis]

On 3/1/22 23:32, Chaitanya Kulkarni wrote:
> Nikos,
> 
>>> [8] https://kernel.dk/io_uring.pdf
>>
>> I would like to participate in the discussion too.
>>
>> The dm-clone target would also benefit from copy offload, as it heavily
>> employs dm-kcopyd. I have been exploring redesigning kcopyd in order to
>> achieve increased IOPS in dm-clone and dm-snapshot for small copies over
>> NVMe devices, but copy offload sounds even more promising, especially
>> for larger copies happening in the background (as is the case with
>> dm-clone's background hydration).
>>
>> Thanks,
>> Nikos
> 
> If you can document your findings here it will be great for me to
> add it to the agenda.
> 

Hi,

Give me a few days to gather my notes, because it's been a while since
the last time I worked on this, and I will come back with a summary of
my findings.

Nikos

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nikos Tsironis]

On 1/27/22 09:14, Chaitanya Kulkarni wrote:
> Hi,
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
> 
> * Problem :-
> -----------------------------------------------------------------------
> 
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
> 
> * Current state of the work :-
> -----------------------------------------------------------------------
> 
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
> 
> We have conducted a call with interested people late last year since
> lack of LSFMMM and we would like to share the details with broader
> community members.
> 
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> -----------------------------------------------------------------------
> 
> With the rise of the SNIA Computational Storage TWG and solutions [2],
> existing SCSI XCopy support in the protocol, recent advancement in the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
> 
> With this background we have significant number of use-cases which are
> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
> Offload support, so that Linux Kernel Storage subsystem can to address
> previously mentioned problems [1] and allow efficient offloading of the
> data related operations. (Such as move/copy etc.)
> 
> For reference following is the list of the use-cases/candidates waiting
> for Copy Offload support :-
> 
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
> 
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> -----------------------------------------------------------------------
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
> 
> Required attendees :-
> 
> Martin K. Petersen
> Jens Axboe
> Christoph Hellwig
> Bart Van Assche
> Zach Brown
> Roland Dreier
> Ric Wheeler
> Trond Myklebust
> Mike Snitzer
> Keith Busch
> Sagi Grimberg
> Hannes Reinecke
> Frederick Knight
> Mikulas Patocka
> Keith Busch
> 
> -ck
> 
> [1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
> [2] https://www.snia.org/computational
> https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
>         https://www.eideticom.com/products.html
> https://www.xilinx.com/applications/data-center/computational-storage.html
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
> [4] https://www.spinics.net/lists/linux-block/msg00599.html
> [5] https://lwn.net/Articles/793585/
> [6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
> namespaces-zns-as-go-to-industry-technology/
> [7] https://github.com/sbates130272/linux-p2pmem
> [8] https://kernel.dk/io_uring.pdf

I would like to participate in the discussion too.

The dm-clone target would also benefit from copy offload, as it heavily
employs dm-kcopyd. I have been exploring redesigning kcopyd in order to
achieve increased IOPS in dm-clone and dm-snapshot for small copies over
NVMe devices, but copy offload sounds even more promising, especially
for larger copies happening in the background (as is the case with
dm-clone's background hydration).

Thanks,
Nikos

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[David Disseldorp]

On Thu, 27 Jan 2022 07:14:13 +0000, Chaitanya Kulkarni wrote:

> Hi,
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
> 
> * Problem :-
> -----------------------------------------------------------------------
> 
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
> 
> * Current state of the work :-
> -----------------------------------------------------------------------
> 
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
> 
> We have conducted a call with interested people late last year since 
> lack of LSFMMM and we would like to share the details with broader
> community members.
> 
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> -----------------------------------------------------------------------
> 
> With the rise of the SNIA Computational Storage TWG and solutions [2],
> existing SCSI XCopy support in the protocol, recent advancement in the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
> 
> With this background we have significant number of use-cases which are
> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
> Offload support, so that Linux Kernel Storage subsystem can to address
> previously mentioned problems [1] and allow efficient offloading of the
> data related operations. (Such as move/copy etc.)
> 
> For reference following is the list of the use-cases/candidates waiting
> for Copy Offload support :-
> 
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
> 
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> -----------------------------------------------------------------------
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.

I'd like to attend this discussion. I've worked on the LIO XCOPY
implementation in drivers/target/target_core_xcopy.c and added Samba's
FSCTL_SRV_COPYCHUNK/FSCTL_DUPLICATE_EXTENTS_TO_FILE support.

Cheers, David

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nitesh Shetty]

Chaitanya,

I would like to join the conversation.

Thanks,
Nitesh

On Sun, Feb 6, 2022 at 7:29 PM Javier González <javier@javigon.com> wrote:
>
> On 27.01.2022 07:14, Chaitanya Kulkarni wrote:
> >Hi,
> >
> >* Background :-
> >-----------------------------------------------------------------------
> >
> >Copy offload is a feature that allows file-systems or storage devices
> >to be instructed to copy files/logical blocks without requiring
> >involvement of the local CPU.
> >
> >With reference to the RISC-V summit keynote [1] single threaded
> >performance is limiting due to Denard scaling and multi-threaded
> >performance is slowing down due Moore's law limitations. With the rise
> >of SNIA Computation Technical Storage Working Group (TWG) [2],
> >offloading computations to the device or over the fabrics is becoming
> >popular as there are several solutions available [2]. One of the common
> >operation which is popular in the kernel and is not merged yet is Copy
> >offload over the fabrics or on to the device.
> >
> >* Problem :-
> >-----------------------------------------------------------------------
> >
> >The original work which is done by Martin is present here [3]. The
> >latest work which is posted by Mikulas [4] is not merged yet. These two
> >approaches are totally different from each other. Several storage
> >vendors discourage mixing copy offload requests with regular READ/WRITE
> >I/O. Also, the fact that the operation fails if a copy request ever
> >needs to be split as it traverses the stack it has the unfortunate
> >side-effect of preventing copy offload from working in pretty much
> >every common deployment configuration out there.
> >
> >* Current state of the work :-
> >-----------------------------------------------------------------------
> >
> >With [3] being hard to handle arbitrary DM/MD stacking without
> >splitting the command in two, one for copying IN and one for copying
> >OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> >candidate. Also, with [4] there is an unresolved problem with the
> >two-command approach about how to handle changes to the DM layout
> >between an IN and OUT operations.
> >
> >We have conducted a call with interested people late last year since
> >lack of LSFMMM and we would like to share the details with broader
> >community members.
>
> Chaitanya,
>
> I would also like to join the F2F conversation as a follow up of the
> virtual one last year. We will have a first version of the patches
> posted in the next few weeks. This will hopefully serve as a good first
> step.
>
> Adding Kanchan to thread too.
>
> Javier


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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Kanchan Joshi]

On Thu, Jan 27, 2022 at 12:51 PM Chaitanya Kulkarni
<chaitanyak@nvidia.com> wrote:
>
> Hi,
>
> * Background :-
> -----------------------------------------------------------------------
>
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
>
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
>
> * Problem :-
> -----------------------------------------------------------------------
>
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
>
> * Current state of the work :-
> -----------------------------------------------------------------------
>
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
>
> We have conducted a call with interested people late last year since
> lack of LSFMMM and we would like to share the details with broader
> community members.

I'm keen on this topic and would like to join the F2F discussion.
The Novmber call did establish some consensus on requirements.
Planning to have a round or two of code-discussions soon.


Thanks,
-- 
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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Luis Chamberlain]

> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> -----------------------------------------------------------------------
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.

Consider me intersted in this topic.

  Luis

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Bart Van Assche]

On 1/26/22 23:14, Chaitanya Kulkarni wrote:
> [1]https://content.riscv.org/wp-content/uploads/2018/12/A-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf
> [2] https://www.snia.org/computational
> https://www.napatech.com/support/resources/solution-descriptions/napatech-smartnic-solution-for-hardware-offload/
>         https://www.eideticom.com/products.html
> https://www.xilinx.com/applications/data-center/computational-storage.html
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
> [4] https://www.spinics.net/lists/linux-block/msg00599.html
> [5] https://lwn.net/Articles/793585/
> [6] https://nvmexpress.org/new-nvmetm-specification-defines-zoned-
> namespaces-zns-as-go-to-industry-technology/
> [7] https://github.com/sbates130272/linux-p2pmem
> [8] https://kernel.dk/io_uring.pdf

Please consider adding the following link to the above list:
https://github.com/bvanassche/linux-kernel-copy-offload

Thanks,

Bart.

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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Johannes Thumshirn]

On Fri, 2022-01-28 at 19:59 +0000, Adam Manzanares wrote:
> On Thu, Jan 27, 2022 at 07:14:13AM +0000, Chaitanya Kulkarni wrote:
> > 
> > * Current state of the work :-
> > -------------------------------------------------------------------
> > ----
> > 
> > With [3] being hard to handle arbitrary DM/MD stacking without
> > splitting the command in two, one for copying IN and one for
> > copying
> > OUT. Which is then demonstrated by the [4] why [3] it is not a
> > suitable
> > candidate. Also, with [4] there is an unresolved problem with the
> > two-command approach about how to handle changes to the DM layout
> > between an IN and OUT operations.
> > 
> > We have conducted a call with interested people late last year
> > since 
> > lack of LSFMMM and we would like to share the details with broader
> > community members.
> 
> Was on that call and I am interested in joining this discussion.

Same for me :)




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Re: [dm-devel] [LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Adam Manzanares]

On Thu, Jan 27, 2022 at 07:14:13AM +0000, Chaitanya Kulkarni wrote:
> Hi,
> 
> * Background :-
> -----------------------------------------------------------------------
> 
> Copy offload is a feature that allows file-systems or storage devices
> to be instructed to copy files/logical blocks without requiring
> involvement of the local CPU.
> 
> With reference to the RISC-V summit keynote [1] single threaded
> performance is limiting due to Denard scaling and multi-threaded
> performance is slowing down due Moore's law limitations. With the rise
> of SNIA Computation Technical Storage Working Group (TWG) [2],
> offloading computations to the device or over the fabrics is becoming
> popular as there are several solutions available [2]. One of the common
> operation which is popular in the kernel and is not merged yet is Copy
> offload over the fabrics or on to the device.
> 
> * Problem :-
> -----------------------------------------------------------------------
> 
> The original work which is done by Martin is present here [3]. The
> latest work which is posted by Mikulas [4] is not merged yet. These two
> approaches are totally different from each other. Several storage
> vendors discourage mixing copy offload requests with regular READ/WRITE
> I/O. Also, the fact that the operation fails if a copy request ever
> needs to be split as it traverses the stack it has the unfortunate
> side-effect of preventing copy offload from working in pretty much
> every common deployment configuration out there.
> 
> * Current state of the work :-
> -----------------------------------------------------------------------
> 
> With [3] being hard to handle arbitrary DM/MD stacking without
> splitting the command in two, one for copying IN and one for copying
> OUT. Which is then demonstrated by the [4] why [3] it is not a suitable
> candidate. Also, with [4] there is an unresolved problem with the
> two-command approach about how to handle changes to the DM layout
> between an IN and OUT operations.
> 
> We have conducted a call with interested people late last year since 
> lack of LSFMMM and we would like to share the details with broader
> community members.

Was on that call and I am interested in joining this discussion.

> 
> * Why Linux Kernel Storage System needs Copy Offload support now ?
> -----------------------------------------------------------------------
> 
> With the rise of the SNIA Computational Storage TWG and solutions [2],
> existing SCSI XCopy support in the protocol, recent advancement in the
> Linux Kernel File System for Zoned devices (Zonefs [5]), Peer to Peer
> DMA support in the Linux Kernel mainly for NVMe devices [7] and
> eventually NVMe Devices and subsystem (NVMe PCIe/NVMeOF) will benefit
> from Copy offload operation.
> 
> With this background we have significant number of use-cases which are
> strong candidates waiting for outstanding Linux Kernel Block Layer Copy
> Offload support, so that Linux Kernel Storage subsystem can to address
> previously mentioned problems [1] and allow efficient offloading of the
> data related operations. (Such as move/copy etc.)
> 
> For reference following is the list of the use-cases/candidates waiting
> for Copy Offload support :-
> 
> 1. SCSI-attached storage arrays.
> 2. Stacking drivers supporting XCopy DM/MD.
> 3. Computational Storage solutions.
> 7. File systems :- Local, NFS and Zonefs.
> 4. Block devices :- Distributed, local, and Zoned devices.
> 5. Peer to Peer DMA support solutions.
> 6. Potentially NVMe subsystem both NVMe PCIe and NVMeOF.
> 
> * What we will discuss in the proposed session ?
> -----------------------------------------------------------------------
> 
> I'd like to propose a session to go over this topic to understand :-
> 
> 1. What are the blockers for Copy Offload implementation ?
> 2. Discussion about having a file system interface.
> 3. Discussion about having right system call for user-space.
> 4. What is the right way to move this work forward ?
> 5. How can we help to contribute and move this work forward ?
> 
> * Required Participants :-
> -----------------------------------------------------------------------
> 
> I'd like to invite file system, block layer, and device drivers
> developers to:-
> 
> 1. Share their opinion on the topic.
> 2. Share their experience and any other issues with [4].
> 3. Uncover additional details that are missing from this proposal.
> 
> Required attendees :-
> 
> Martin K. Petersen
> Jens Axboe
> Christoph Hellwig
> Bart Van Assche
> Zach Brown
> Roland Dreier
> Ric Wheeler
> Trond Myklebust
> Mike Snitzer
> Keith Busch
> Sagi Grimberg
> Hannes Reinecke
> Frederick Knight
> Mikulas Patocka
> Keith Busch
> 
> -ck
> 
> [1]https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=3933d1bc-66a8e8f3-39325af3-0cc47a30d446-55df181e6aabd8e8&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fcontent.riscv.org*2Fwp-content*2Fuploads*2F2018*2F12*2FA-New-Golden-Age-for-Computer-Architecture-History-Challenges-and-Opportunities-David-Patterson-.pdf__;JSUlJSUlJSU!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggCI71vV3$ 
> [2] https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=e9dc0639-b6473f76-e9dd8d76-0cc47a30d446-03d65bc9ad20d215&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fwww.snia.org*2Fcomputational__;JSUlJQ!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggLInnHhS$ 
> https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=13eb47ed-4c707ea2-13eacca2-0cc47a30d446-3d06014a33154497&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fwww.napatech.com*2Fsupport*2Fresources*2Fsolution-descriptions*2Fnapatech-smartnic-solution-for-hardware-offload*2F__;JSUlJSUlJSU!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggJJSlhVh$ 
>        https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=8ba72fbf-d43c16f0-8ba6a4f0-0cc47a30d446-359457fd63a1a13d&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fwww.eideticom.com*2Fproducts.html__;JSUlJQ!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggGCerEbv$ 
> https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=75b96fa9-2a2256e6-75b8e4e6-0cc47a30d446-0403b00d6ff1bab8&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fwww.xilinx.com*2Fapplications*2Fdata-center*2Fcomputational-storage.html__;JSUlJSUl!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggK0Hp6vG$ 
> [3] git://git.kernel.org/pub/scm/linux/kernel/git/mkp/linux.git xcopy
> [4] https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=3a49563e-65d26f71-3a48dd71-0cc47a30d446-3cecc3d55115742b&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fwww.spinics.net*2Flists*2Flinux-block*2Fmsg00599.html__;JSUlJSUl!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggPvo936U$ 
> [5] https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=910e6991-ce9550de-910fe2de-0cc47a30d446-c412c0c3c4c51c2b&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Flwn.net*2FArticles*2F793585*2F__;JSUlJSUl!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggIprHJMJ$ 
> [6] https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=0ab886e2-5523bfad-0ab90dad-0cc47a30d446-df0ae4acca6d59f2&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fnvmexpress.org*2Fnew-nvmetm-specification-defines-zoned-__;JSUlJQ!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggB4MUwfa$ 
> namespaces-zns-as-go-to-industry-technology/
> [7] https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=44a1a51b-1b3a9c54-44a02e54-0cc47a30d446-8577b144c92493eb&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fgithub.com*2Fsbates130272*2Flinux-p2pmem__;JSUlJSU!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggEa99Fso$ 
> [8] https://urldefense.com/v3/__https://protect2.fireeye.com/v1/url?k=0745845d-58debd12-07440f12-0cc47a30d446-53178030a251a9d8&q=1&e=c880f1d4-0275-4c86-ba38-205de0f24f69&u=https*3A*2F*2Fkernel.dk*2Fio_uring.pdf__;JSUlJQ!!EwVzqGoTKBqv-0DWAJBm!BhtIUewpIpaTRbAVe6VvjiRs-431N4ehiLybkoGuMxLiIvcuYlijJGJWlXVggJUxR2B3$ 


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