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

Anna Schumaker
2015-07-10T19:21:58Z

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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