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Date: Sun, 28 Jan 2018 14:57:35 +0100
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc: Network Development <netdev@...r.kernel.org>,
David Miller <davem@...emloft.net>, rds-devel@....oracle.com,
santosh.shilimkar@...cle.com
Subject: Re: [PATCH net-next 5/7] rds: zerocopy Tx support.
On Wed, Jan 24, 2018 at 12:46 PM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> If the MSG_ZEROCOPY flag is specified with rds_sendmsg(), and,
> if the SO_ZEROCOPY socket option has been set on the PF_RDS socket,
> application pages sent down with rds_sendmsg() are pinned.
>
> The pinning uses the accounting infrastructure added by
> Commit a91dbff551a6 ("sock: ulimit on MSG_ZEROCOPY pages")
>
> The payload bytes in the message may not be modified for the
> duration that the message has been pinned. A multi-threaded
> application using this infrastructure may thus need to be notified
> about send-completion so that it can free/reuse the buffers
> passed to rds_sendmsg(). Notification of send-completion will
> identify each message-buffer by a cookie that the application
> must specify as ancillary data to rds_sendmsg().
> The ancillary data in this case has cmsg_level == SOL_RDS
> and cmsg_type == RDS_CMSG_ZCOPY_COOKIE.
>
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
> include/uapi/linux/rds.h | 1 +
> net/rds/message.c | 48 +++++++++++++++++++++++++++++++++++++++++++++-
> net/rds/rds.h | 3 +-
> net/rds/send.c | 44 ++++++++++++++++++++++++++++++++++++-----
> 4 files changed, 88 insertions(+), 8 deletions(-)
>
> diff --git a/include/uapi/linux/rds.h b/include/uapi/linux/rds.h
> index e71d449..12e3bca 100644
> --- a/include/uapi/linux/rds.h
> +++ b/include/uapi/linux/rds.h
> @@ -103,6 +103,7 @@
> #define RDS_CMSG_MASKED_ATOMIC_FADD 8
> #define RDS_CMSG_MASKED_ATOMIC_CSWP 9
> #define RDS_CMSG_RXPATH_LATENCY 11
> +#define RDS_CMSG_ZCOPY_COOKIE 12
>
> #define RDS_INFO_FIRST 10000
> #define RDS_INFO_COUNTERS 10000
> diff --git a/net/rds/message.c b/net/rds/message.c
> index 7ca968a..79b24db 100644
> --- a/net/rds/message.c
> +++ b/net/rds/message.c
> @@ -362,12 +362,14 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
> return rm;
> }
>
> -int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from)
> +int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from,
> + bool zcopy)
> {
> unsigned long to_copy, nbytes;
> unsigned long sg_off;
> struct scatterlist *sg;
> int ret = 0;
> + int length = iov_iter_count(from);
>
> rm->m_inc.i_hdr.h_len = cpu_to_be32(iov_iter_count(from));
>
> @@ -377,6 +379,50 @@ int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from)
> sg = rm->data.op_sg;
> sg_off = 0; /* Dear gcc, sg->page will be null from kzalloc. */
>
> + if (zcopy) {
> + int total_copied = 0;
> + struct sk_buff *skb;
> +
> + skb = alloc_skb(SO_EE_ORIGIN_MAX_ZCOOKIES * sizeof(u32),
> + GFP_KERNEL);
> + if (!skb)
> + return -ENOMEM;
> + rm->data.op_mmp_znotifier = RDS_ZCOPY_SKB(skb);
> + memset(rm->data.op_mmp_znotifier, 0,
> + sizeof(*rm->data.op_mmp_znotifier));
> + if (mm_account_pinned_pages(&rm->data.op_mmp_znotifier->z_mmp,
> + length)) {
> + consume_skb(skb);
> + rm->data.op_mmp_znotifier = NULL;
> + return -ENOMEM;
> + }
> + while (iov_iter_count(from)) {
> + struct page *pages;
> + size_t start;
> + ssize_t copied;
> +
> + copied = iov_iter_get_pages(from, &pages, PAGE_SIZE,
> + 1, &start);
> + if (copied < 0) {
> + struct mmpin *mmp;
> +
> + mmp = &rm->data.op_mmp_znotifier->z_mmp;
> + mm_unaccount_pinned_pages(mmp);
> + consume_skb(skb);
> + rm->data.op_mmp_znotifier = NULL;
> + return -EFAULT;
also need to unmap pages pinned during previous iterations.
> + }
> + total_copied += copied;
> + iov_iter_advance(from, copied);
> + length -= copied;
> + sg_set_page(sg, pages, copied, start);
> + rm->data.op_nents++;
> + sg++;
> + }
> + WARN_ON_ONCE(length != 0);
> + return ret;
> + } /* zcopy */
> +
> while (iov_iter_count(from)) {
> if (!sg_page(sg)) {
> ret = rds_page_remainder_alloc(sg, iov_iter_count(from),
> diff --git a/net/rds/rds.h b/net/rds/rds.h
> index c375dd8..9dfc23c 100644
> --- a/net/rds/send.c
> +++ b/net/rds/send.c
> @@ -875,12 +875,13 @@ static int rds_send_queue_rm(struct rds_sock *rs, struct rds_connection *conn,
> * rds_message is getting to be quite complicated, and we'd like to allocate
> * it all in one go. This figures out how big it needs to be up front.
> */
> -static int rds_rm_size(struct msghdr *msg, int data_len)
> +static int rds_rm_size(struct msghdr *msg, int data_len, int num_sgs)
> {
> struct cmsghdr *cmsg;
> int size = 0;
> int cmsg_groups = 0;
> int retval;
> + bool zcopy_cookie = false;
>
> for_each_cmsghdr(cmsg, msg) {
> if (!CMSG_OK(msg, cmsg))
> @@ -899,6 +900,8 @@ static int rds_rm_size(struct msghdr *msg, int data_len)
>
> break;
>
> + case RDS_CMSG_ZCOPY_COOKIE:
> + zcopy_cookie = true;
> case RDS_CMSG_RDMA_DEST:
> case RDS_CMSG_RDMA_MAP:
> cmsg_groups |= 2;
> @@ -919,7 +922,10 @@ static int rds_rm_size(struct msghdr *msg, int data_len)
>
> }
>
> - size += ceil(data_len, PAGE_SIZE) * sizeof(struct scatterlist);
> + if ((msg->msg_flags & MSG_ZEROCOPY) && !zcopy_cookie)
> + return -EINVAL;
> +
> + size += num_sgs * sizeof(struct scatterlist);
argument data_len is no longer used
>
> /* Ensure (DEST, MAP) are never used with (ARGS, ATOMIC) */
> if (cmsg_groups == 3)
> @@ -928,6 +934,18 @@ static int rds_rm_size(struct msghdr *msg, int data_len)
> return size;
> }
>
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