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    SubjectRe: [PATCH v3 4/4] io_uring: add support for zone-append
    On Fri, Jul 10, 2020 at 6:59 PM Kanchan Joshi <joshiiitr@gmail.com> wrote:
    >
    > On Fri, Jul 10, 2020 at 6:39 PM Christoph Hellwig <hch@infradead.org> wrote:
    > >
    > > On Thu, Jul 09, 2020 at 12:50:27PM -0600, Jens Axboe wrote:
    > > > It might, if you have IRQ context for the completion. task_work isn't
    > > > expensive, however. It's not like a thread offload.

    Not sure about polled-completion but we have IRQ context for regular completion.
    If I've got it right, I need to store task_struct during submission,
    and use that to register a task_work during completion. At some point
    when this task_work gets called it will update the user-space pointer
    with the result.
    It can be the case that we get N completions parallely, but they all
    would get serialized because all N task-works need to be executed in
    the context of single task/process?

    > > > > Using flags have not been liked here, but given the upheaval involved so
    > > > > far I have begun to feel - it was keeping things simple. Should it be
    > > > > reconsidered?
    > > >
    > > > It's definitely worth considering, especially since we can use cflags
    > > > like Pavel suggested upfront and not need any extra storage. But it
    > > > brings us back to the 32-bit vs 64-bit discussion, and then using blocks
    > > > instead of bytes. Which isn't exactly super pretty.
    > >
    > > block doesn't work for the case of writes to files that don't have
    > > to be aligned in any way. And that I think is the more broadly
    > > applicable use case than zone append on block devices.
    >
    > But when can it happen that we do zone-append on a file (zonefs I
    > asssume), and device returns a location (write-pointer essentially)
    > which is not in multiple of 512b?
    >
    >
    > --
    > Joshi



    --
    Joshi

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