Date: Tue, 23 Sep 2014 15:55:18 -0400
From: "'J. Bruce Fields'" <bfields@fieldses.org>
To: Steve Wise <swise@opengridcomputing.com>
Cc: "'Chuck Lever'" <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org,
        linux-rdma@vger.kernel.org
Subject: Re: [PATCH V2] svcrdma: Advertise the correct max payload
Message-ID: <20140923195518.GN29932@fieldses.org>
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On Tue, Sep 23, 2014 at 02:53:28PM -0500, Steve Wise wrote:
> 
> 
> > -----Original Message-----
> > From: 'J. Bruce Fields' [mailto:bfields@fieldses.org]
> > Sent: Tuesday, September 23, 2014 2:48 PM
> > To: Steve Wise
> > Cc: 'Chuck Lever'; linux-nfs@vger.kernel.org; linux-rdma@vger.kernel.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; })
>