Re: [RFC PATCH 4/4] ksmbd: send READ payloads with MSG_SPLICE_PAGES

[Namjae Jeon]

> @@ -35,6 +35,47 @@ bool ksmbd_queue_request(struct ksmbd_work *work, bool use_write_wq)
>         return queue_work(wq, &work->work);
>  }
>
> +struct aux_read *ksmbd_alloc_read_buf(size_t length, bool allow_splice)
> +{
> +       struct aux_read *ar;
> +       size_t alloc_size = ALIGN(length, 8);
> +
> +       ar = kzalloc_obj(*ar, KSMBD_DEFAULT_GFP);
> +       if (!ar)
> +               return NULL;
> +
> +       if (allow_splice && length) {
> +               unsigned int order = get_order(alloc_size);
> +
> +               /* TCP references to tails must keep the whole allocation alive. */
> +               if (order <= MAX_PAGE_ORDER)
> +                       ar->page = alloc_pages(GFP_KERNEL | __GFP_COMP |
> +                                              __GFP_NORETRY | __GFP_NOWARN, order);
Order-8 and order-10 allocations can easily fail when memory is
fragmented. Since MSG_SPLICE_PAGES does not require physically
contiguous pages, could we allocate individual pages and use a bvec
iterator instead? Please see drivers/nvme/host/tcp.c as an example.

> +       }
> +       if (ar->page)
> +               ar->buf = page_address(ar->page);
> +       else
> +               ar->buf = kvmalloc(alloc_size, KSMBD_DEFAULT_GFP);
> +       if (!ar->buf) {
> +               kfree(ar);
> +               return NULL;
> +       }
> +       return ar;
> +}
> +

> @@ -47,6 +49,29 @@
>  #include "transport_tcp.h"
>  #include "compress.h"
>
> +/* Switching affects allocation, not ownership of existing READ buffers. */
> +static bool read_splice;
> +
> +static int read_splice_set(const char *val, const struct kernel_param *kp)
> +{
> +       bool enabled;
> +       int ret;
> +
> +       ret = kstrtobool(val ?: "1", &enabled);
> +       if (!ret)
> +               WRITE_ONCE(*(bool *)kp->arg, enabled);
> +       return ret;
> +}
> +
> +static const struct kernel_param_ops read_splice_ops = {
> +       .flags = KERNEL_PARAM_OPS_FL_NOARG,
> +       .set = read_splice_set,
> +       .get = param_get_bool,
> +};
> +module_param_cb(read_splice, &read_splice_ops, &read_splice, 0644);
> +__MODULE_PARM_TYPE(read_splice, "bool");
> +MODULE_PARM_DESC(read_splice, "Page-backed ordinary TCP READ sends");
Can we set enable/disable it via ksmbd.conf also ?