Re: [RFC PATCH v2 0/2] introduce io_uring_cmd_import_fixed_vec

[Sidong Yang <sidong.yang@furiosa.ai>]

On Thu, Mar 13, 2025 at 08:01:15AM -0600, Jens Axboe wrote:
> On 3/13/25 7:56 AM, Sidong Yang wrote:
> > On Thu, Mar 13, 2025 at 01:17:44PM +0000, Pavel Begunkov wrote:
> >> On 3/13/25 13:15, Pavel Begunkov wrote:
> >>> On 3/13/25 10:44, Sidong Yang wrote:
> >>>> On Thu, Mar 13, 2025 at 08:57:45AM +0000, Pavel Begunkov wrote:
> >>>>> On 3/12/25 14:23, Sidong Yang wrote:
> >>>>>> This patche series introduce io_uring_cmd_import_vec. With this function,
> >>>>>> Multiple fixed buffer could be used in uring cmd. It's vectored version
> >>>>>> for io_uring_cmd_import_fixed(). Also this patch series includes a usage
> >>>>>> for new api for encoded read in btrfs by using uring cmd.
> >>>>>
> >>>>> Pretty much same thing, we're still left with 2 allocations in the
> >>>>> hot path. What I think we can do here is to add caching on the
> >>>>> io_uring side as we do with rw / net, but that would be invisible
> >>>>> for cmd drivers. And that cache can be reused for normal iovec imports.
> >>>>>
> >>>>> https://github.com/isilence/linux.git regvec-import-cmd
> >>>>> (link for convenience)
> >>>>> https://github.com/isilence/linux/tree/regvec-import-cmd
> >>>>>
> >>>>> Not really target tested, no btrfs, not any other user, just an idea.
> >>>>> There are 4 patches, but the top 3 are of interest.
> >>>>
> >>>> Thanks, I justed checked the commits now. I think cache is good to resolve
> >>>> this without allocation if cache hit. Let me reimpl this idea and test it
> >>>> for btrfs.
> >>>
> >>> Sure, you can just base on top of that branch, hashes might be
> >>> different but it's identical to the base it should be on. Your
> >>> v2 didn't have some more recent merged patches.
> >>
> >> Jens' for-6.15/io_uring-reg-vec specifically, but for-next likely
> >> has it merged.
> > 
> > Yes, there is commits about io_uring-reg-vec in Jens' for-next. I'll
> > make v3 based on the branch.
> 
> Basing patches on that is fine, just never base branches on it. My
> for-next branch is just a merge point for _everything_ that's queued for
> the next release, io_uring and block related. The right branch to base
> on for this case would be for-6.15/io_uring-reg-vec, which is also in my
> for-next branch.

Agreed, for-6.15/io_uring-reg-vec is the right base branch for this. 

Thanks,
Sidong
> 
> This is more of a FYI than anything, as you're not doing a pull request.
> Using for-next for patches is fine.
> 
> -- 
> Jens Axboe