Re: [PATCH] svcrdma: Advertise the correct max payload

["J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>]

On Mon, Sep 22, 2014 at 01:36:53PM -0500, Steve Wise wrote:
> Svcrdma currently advertises 1MB, which is too large.  The correct value
> is the max scatter-gather allowed in an NFSRDMA IO chunk * the host page
> size. This bug is usually benign because the Linux X64 NFSRDMA client
> correctly limits the payload size to the correct value (64*4096 = 256KB).
> But if the Linux client is PPC64 with a 64KB page size, then the client
> will indeed use a payload size that will overflow the server.
> 
> Signed-off-by: Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>
> ---
> 
>  net/sunrpc/xprtrdma/svc_rdma_transport.c |    2 +-
>  net/sunrpc/xprtrdma/xprt_rdma.h          |    2 ++
>  2 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> index 374feb4..4e61880 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> @@ -91,7 +91,7 @@ struct svc_xprt_class svc_rdma_class = {
>  	.xcl_name = "rdma",
>  	.xcl_owner = THIS_MODULE,
>  	.xcl_ops = &svc_rdma_ops,
> -	.xcl_max_payload = RPCSVC_MAXPAYLOAD_TCP,
> +	.xcl_max_payload = RPCSVC_MAXPAYLOAD_RDMA,
>  	.xcl_ident = XPRT_TRANSPORT_RDMA,
>  };
>  
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index c419498..467a77c 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -392,4 +392,6 @@ extern struct kmem_cache *svc_rdma_ctxt_cachep;
>  /* Workqueue created in svc_rdma.c */
>  extern struct workqueue_struct *svc_rdma_wq;
>  
> +#define RPCSVC_MAXPAYLOAD_RDMA	(RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT)

Do you want to define this as the minimum of this and
RPCSVC_MAXPAYLOAD_TCP, in case RPCRDMA_MAX_DATA_SEGS gets increased some
day?

--b.

> +
>  #endif				/* _LINUX_SUNRPC_XPRT_RDMA_H */
> 
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