Re: [PATCH v2 08/12] io_uring: overflow processing for CQE32

[Kanchan Joshi <joshiiitr@gmail.com>]

On Thu, Apr 21, 2022 at 1:37 PM Stefan Roesch <shr@fb.com> wrote:
>
> This adds the overflow processing for large CQE's.
>
> This adds two parameters to the io_cqring_event_overflow function and
> uses these fields to initialize the large CQE fields.
>
> Allocate enough space for large CQE's in the overflow structue. If no
> large CQE's are used, the size of the allocation is unchanged.
>
> The cqe field can have a different size depending if its a large
> CQE or not. To be able to allocate different sizes, the two fields
> in the structure are re-ordered.
>
> Co-developed-by: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Stefan Roesch <shr@fb.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  fs/io_uring.c | 26 +++++++++++++++++++-------
>  1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index ff6229b6df16..50efced63ec9 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -220,8 +220,8 @@ struct io_mapped_ubuf {
>  struct io_ring_ctx;
>
>  struct io_overflow_cqe {
> -       struct io_uring_cqe cqe;
>         struct list_head list;
> +       struct io_uring_cqe cqe;
>  };
>
>  struct io_fixed_file {
> @@ -2016,13 +2016,17 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
>         while (!list_empty(&ctx->cq_overflow_list)) {
>                 struct io_uring_cqe *cqe = io_get_cqe(ctx);
>                 struct io_overflow_cqe *ocqe;
> +               size_t cqe_size = sizeof(struct io_uring_cqe);
> +
> +               if (ctx->flags & IORING_SETUP_CQE32)
> +                       cqe_size <<= 1;
>
>                 if (!cqe && !force)
>                         break;
>                 ocqe = list_first_entry(&ctx->cq_overflow_list,
>                                         struct io_overflow_cqe, list);
>                 if (cqe)
> -                       memcpy(cqe, &ocqe->cqe, sizeof(*cqe));
> +                       memcpy(cqe, &ocqe->cqe, cqe_size);
>                 else
>                         io_account_cq_overflow(ctx);
>
> @@ -2111,11 +2115,15 @@ static __cold void io_uring_drop_tctx_refs(struct task_struct *task)
>  }
>
>  static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
> -                                    s32 res, u32 cflags)
> +                                    s32 res, u32 cflags, u64 extra1, u64 extra2)
>  {
>         struct io_overflow_cqe *ocqe;
> +       size_t ocq_size = sizeof(struct io_overflow_cqe);
>
> -       ocqe = kmalloc(sizeof(*ocqe), GFP_ATOMIC | __GFP_ACCOUNT);
> +       if (ctx->flags & IORING_SETUP_CQE32)

This can go inside in a bool variable, as this check is repeated in
this function.