Re: [PATCH v1 02/12] xprtrdma: Raise maximum payload size to one megabyte

[Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>]

Hi Chuck,

On 07/09/2015 04:41 PM, Chuck Lever wrote:
> The point of larger rsize and wsize is to reduce the per-byte cost
> of memory registration and deregistration. Modern HCAs can typically
> handle a megabyte or more with a single registration operation.
> 
> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
>  net/sunrpc/xprtrdma/xprt_rdma.h |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index f49dd8b..abee472 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -165,8 +165,7 @@ rdmab_to_msg(struct rpcrdma_regbuf *rb)
>   * struct rpcrdma_buffer. N is the max number of outstanding requests.
>   */
>  
> -/* temporary static scatter/gather max */
> -#define RPCRDMA_MAX_DATA_SEGS	(64)	/* max scatter/gather */
> +#define RPCRDMA_MAX_DATA_SEGS	((1 * 1024 * 1024) / PAGE_SIZE)
                                         ^^^
What is the significance of the 1 here?

Thanks,
Anna

>  #define RPCRDMA_MAX_SEGS 	(RPCRDMA_MAX_DATA_SEGS + 2) /* head+tail = 2 */
>  
>  struct rpcrdma_buffer;
> 
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