Re: [PATCH 1/3] io_uring/net: only import send_zc buffer once

[Caleb Sander Mateos <csander@purestorage.com>]

On Fri, Mar 21, 2025 at 1:37 PM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> On 3/21/25 18:48, Caleb Sander Mateos wrote:
> > io_send_zc() guards its call to io_send_zc_import() with if (!done_io)
> > in an attempt to avoid calling it redundantly on the same req. However,
> > if the initial non-blocking issue returns -EAGAIN, done_io will stay 0.
> > This causes the subsequent issue to unnecessarily re-import the buffer.
> >
> > Add an explicit flag "imported" to io_sr_msg to track if its buffer has
> > already been imported. Clear the flag in io_send_zc_prep(). Call
> > io_send_zc_import() and set the flag in io_send_zc() if it is unset.
>
> lgtm. Maybe there is a way to put it into req->flags and combine
> with REQ_F_IMPORT_BUFFER, but likely just an idea for the future.

Yes, I considered making it a bitflag. But since there was an existing
hole in io_sr_msg, I figured it wasn't worth optimizing. Certainly if
we want to shrink io_sr_msg in the future, this is low-hanging fruit.
I'm a bit hesitant to reserve a bit in the generic req->flags that's
only used for one opcode.

Best,
Caleb