Re: [PATCH V2] svcrdma: Advertise the correct max payload

'J. Bruce Fields'
2014-09-23T19:55:18Z

On Tue, Sep 23, 2014 at 02:53:28PM -0500, Steve Wise wrote:
>
>
> > -----Original Message-----
> > From: 'J. Bruce Fields' [mailto:bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org]
> > Sent: Tuesday, September 23, 2014 2:48 PM
> > To: Steve Wise
> > Cc: 'Chuck Lever'; linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> > Subject: Re: [PATCH V2] svcrdma: Advertise the correct max payload
> >
> > On Tue, Sep 23, 2014 at 02:42:34PM -0500, Steve Wise wrote:
> > >
> > > > > diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> > > > > index c419498..a9cf5c3 100644
> > > > > --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> > > > > +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> > > > > @@ -392,4 +392,8 @@ 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 \
> > > > > + (RPCSVC_MAXPAYLOAD < (RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT) ? \
> > > > > + RPCSVC_MAXPAYLOAD : (RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT))
> > > > > +
> > > >
> > > > Couldn't you use:
> > > >
> > > > #if RPCSVC_MAXPAYLOAD < (RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT)
> > > > #define RPCSVC_MAXPAYLOAD_RDMA RPC_MAXPAYLOAD
> > > > #else
> > > > #define RPCSVC_MAXPAYLOAD_RDMA (RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT)
> > > > #endif
> > > >
> > > > That seems more idiomatic.
> > >
> > > Sure. That makes it easier to read in my opinion too.
> > >
> > > I'll send out V3 with this change.
> >
> > While we're bikeshedding, why not use min()?
> >
> > --b.
>
> I tried that initially. But min() and min_t() don't work because of the way we use the #define. With it defined thusly:

OK, OK. Whatever works.--b.

>
> #define RPCSVC_MAXPAYLOAD_RDMA min(RPC_MAXPAYLOAD, RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT)
>
> I see this error:
>
> CC [M] net/sunrpc/xprtrdma/svc_rdma_transport.o
> net/sunrpc/xprtrdma/svc_rdma_transport.c:94: error: braced-group within expression allowed only inside a function
> make[3]: *** [net/sunrpc/xprtrdma/svc_rdma_transport.o] Error 1
> make[2]: *** [net/sunrpc/xprtrdma] Error 2
> make[1]: *** [net/sunrpc] Error 2
> make: *** [net] Error 2
>
> min() looks like this:
>
> #define min(x, y) ({ \
> typeof(x) _min1 = (x); \
> typeof(y) _min2 = (y); \
> (void) (&_min1 == &_min2); \
> _min1 < _min2 ? _min1 : _min2; })