Re: [PATCH 0/5] optimize some data structure in nvme

[Chaitanya Kulkarni]

On 5/1/23 05:40, Christophe JAILLET wrote:
> This serie is a proposal to slighly optimize the memory needed for some
> structures used in nvme.
>
> This follows the discussion in [1].
>
> Honnestly, I'm not convinced that this serie really brings semething.
> Because of the way memory alocation works, and its over-allocation to try to
> avoid memory fragmentation, some limited gains are most of the time useless.
>
> It could still help:
>     - many holes in structure can, at some point, have its size reach a threshold
>       (this is specially true if such structures are allocated with kcalloc() or
>       kmalloc_array())
>     - it can save some space in some other structures if embedded in them
>     - it can save a few cycles if the structure is memcpy()'ed or zeroed, for
>       example
>     - can reduce cache usage
>
> With that in mind, patch 3 is a win, patch 4 is likely a win, the other ones are
> much more theorical.
>
> The changes are really limited, so even if the gain is marginal, maybe it still
> makes sense to merge them.
>
> Each patch gives the layout generated by pahole before and after the patch.
>
> [1]: https://lore.kernel.org/all/67a9e53e-4ac9-7ba8-9713-96c1dfe1e341@xxxxxxxxxx/
>
> Christophe JAILLET (5):
>    nvmet: Reorder fields in 'struct nvmet_sq'
>    nvmet: Reorder fields in 'struct nvme_ctrl'
>    nvmet: Reorder fields in 'struct nvmf_ctrl_options'
>    nvmet: Reorder fields in 'struct nvme_dhchap_queue_context'
>    nvmet: Reorder fields in 'struct nvmefc_fcp_req'
>
>   drivers/nvme/host/auth.c       |  6 +++---
>   drivers/nvme/host/fabrics.h    |  8 ++++----
>   drivers/nvme/host/nvme.h       |  6 +++---
>   drivers/nvme/target/nvmet.h    |  4 ++--
>   include/linux/nvme-fc-driver.h | 10 +++++-----
>   5 files changed, 17 insertions(+), 17 deletions(-)
>

thanks a lot for doing this and following the comment on the other patch.

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@xxxxxxxxxx>

-ck