[PATCH net-next v15 11/14] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags

[Eric Dumazet]

On Fri, Jun 28, 2024 at 2:33 AM Mina Almasry <almasrymina at google.com> wrote:
>
> Add an interface for the user to notify the kernel that it is done
> reading the devmem dmabuf frags returned as cmsg. The kernel will
> drop the reference on the frags to make them available for reuse.
>
> Signed-off-by: Willem de Bruijn <willemb at google.com>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz at google.com>
> Signed-off-by: Mina Almasry <almasrymina at google.com>
>
> ---
>
> v10:
> - Fix leak of tokens (Nikolay).
>
> v7:
> - Updated SO_DEVMEM_* uapi to use the next available entry (Arnd).
>
> v6:
> - Squash in locking optimizations from edumazet at google.com. With his
>   changes we lock the xarray once per sock_devmem_dontneed operation
>   rather than once per frag.
>
> Changes in v1:
> - devmemtoken -> dmabuf_token (David).
> - Use napi_pp_put_page() for refcounting (Yunsheng).
> - Fix build error with missing socket options on other asms.
>
> ---
>  arch/alpha/include/uapi/asm/socket.h  |  1 +
>  arch/mips/include/uapi/asm/socket.h   |  1 +
>  arch/parisc/include/uapi/asm/socket.h |  1 +
>  arch/sparc/include/uapi/asm/socket.h  |  1 +
>  include/uapi/asm-generic/socket.h     |  1 +
>  include/uapi/linux/uio.h              |  4 ++
>  net/core/sock.c                       | 61 +++++++++++++++++++++++++++
>  7 files changed, 70 insertions(+)
>

>
> +struct dmabuf_token {
> +       __u32 token_start;
> +       __u32 token_count;
> +};
>  /*
>   *     UIO_MAXIOV shall be at least 16 1003.1g (5.4.1.1)
>   */
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 9abc4fe259535..040c66ac26244 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -124,6 +124,7 @@
>  #include <linux/netdevice.h>
>  #include <net/protocol.h>
>  #include <linux/skbuff.h>
> +#include <linux/skbuff_ref.h>
>  #include <net/net_namespace.h>
>  #include <net/request_sock.h>
>  #include <net/sock.h>
> @@ -1049,6 +1050,62 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
>         return 0;
>  }
>
> +#ifdef CONFIG_PAGE_POOL
> +static noinline_for_stack int
> +sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
> +{
> +       unsigned int num_tokens, i, j, k, netmem_num = 0;
> +       struct dmabuf_token *tokens;
> +       netmem_ref netmems[16];
> +       int ret = 0;
> +
> +       if (sk->sk_type != SOCK_STREAM || sk->sk_protocol != IPPROTO_TCP)
> +               return -EBADF;

This might use sk_is_tcp() helper.

> +
> +       if (optlen % sizeof(struct dmabuf_token) ||
> +           optlen > sizeof(*tokens) * 128)
> +               return -EINVAL;
> +
> +       tokens = kvmalloc_array(128, sizeof(*tokens), GFP_KERNEL);

This allocates 8192 bytes even for small optlen ?

Probably no big deal, no need to send a new version.

Reviewed-by: Eric Dumazet <edumazet at google.com>