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

[Javier González]

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