Re: [PATCH] Make RPCRDMA_MAX_RECV_BATCH configurable.

[Chuck Lever <chuck.lever@oracle.com>]

On 11/13/25 4:37 AM, Gaurav Gangalwar wrote:
> Bumped up rpcrdma_max_recv_batch to 64.
> Added param to change to it, it becomes handy to use higher value
> to avoid hung.

[ Resend with correct NFSD reviewer email addresses and linux-rdma@ ]

Hi Gaurav -

Adding an administrative setting is generally a last resort. First,
we want a full root-cause analysis to understand the symptoms you
are trying to address. Do you have an RCA or a simple reproducer to
share with us?


> Signed-off-by: Gaurav Gangalwar <gaurav.gangalwar@gmail.com>
> ---
>  net/sunrpc/xprtrdma/frwr_ops.c           | 2 +-
>  net/sunrpc/xprtrdma/module.c             | 6 ++++++
>  net/sunrpc/xprtrdma/svc_rdma_transport.c | 2 +-
>  net/sunrpc/xprtrdma/verbs.c              | 2 +-
>  net/sunrpc/xprtrdma/xprt_rdma.h          | 4 +---
>  5 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
> index 31434aeb8e29..863a0c567915 100644
> --- a/net/sunrpc/xprtrdma/frwr_ops.c
> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
> @@ -246,7 +246,7 @@ int frwr_query_device(struct rpcrdma_ep *ep, const struct ib_device *device)
>  	ep->re_attr.cap.max_send_wr += 1; /* for ib_drain_sq */
>  	ep->re_attr.cap.max_recv_wr = ep->re_max_requests;
>  	ep->re_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;
> -	ep->re_attr.cap.max_recv_wr += RPCRDMA_MAX_RECV_BATCH;
> +	ep->re_attr.cap.max_recv_wr += rpcrdma_max_recv_batch;
>  	ep->re_attr.cap.max_recv_wr += 1; /* for ib_drain_rq */
>  
>  	ep->re_max_rdma_segs =
> diff --git a/net/sunrpc/xprtrdma/module.c b/net/sunrpc/xprtrdma/module.c
> index 697f571d4c01..afeec5a68151 100644
> --- a/net/sunrpc/xprtrdma/module.c
> +++ b/net/sunrpc/xprtrdma/module.c
> @@ -27,6 +27,12 @@ MODULE_ALIAS("svcrdma");
>  MODULE_ALIAS("xprtrdma");
>  MODULE_ALIAS("rpcrdma6");
>  
> +unsigned int rpcrdma_max_recv_batch = 64;
> +module_param_named(max_recv_batch, rpcrdma_max_recv_batch, uint, 0644);
> +MODULE_PARM_DESC(max_recv_batch,
> +		 "Maximum number of Receive WRs to post in a batch "
> +		 "(default: 64, set to 0 to disable batching)");
> +
>  static void __exit rpc_rdma_cleanup(void)
>  {
>  	xprt_rdma_cleanup();
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> index 3d7f1413df02..32a9ceb18389 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> @@ -440,7 +440,7 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>  	newxprt->sc_max_req_size = svcrdma_max_req_size;
>  	newxprt->sc_max_requests = svcrdma_max_requests;
>  	newxprt->sc_max_bc_requests = svcrdma_max_bc_requests;
> -	newxprt->sc_recv_batch = RPCRDMA_MAX_RECV_BATCH;
> +	newxprt->sc_recv_batch = rpcrdma_max_recv_batch;
>  	newxprt->sc_fc_credits = cpu_to_be32(newxprt->sc_max_requests);
>  
>  	/* Qualify the transport's resource defaults with the
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 63262ef0c2e3..7cd0a2c152e6 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -1359,7 +1359,7 @@ void rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, int needed)
>  	if (likely(ep->re_receive_count > needed))
>  		goto out;
>  	needed -= ep->re_receive_count;
> -	needed += RPCRDMA_MAX_RECV_BATCH;
> +	needed += rpcrdma_max_recv_batch;
>  
>  	if (atomic_inc_return(&ep->re_receiving) > 1)
>  		goto out;
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index 8147d2b41494..1051aa612f36 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -216,9 +216,7 @@ struct rpcrdma_rep {
>   *
>   * Setting this to zero disables Receive post batching.
>   */
> -enum {
> -	RPCRDMA_MAX_RECV_BATCH = 7,
> -};
> +extern unsigned int rpcrdma_max_recv_batch;
>  
>  /* struct rpcrdma_sendctx - DMA mapped SGEs to unmap after Send completes
>   */


-- 
Chuck Lever