Re: [PATCH linux-next v2] SUNRPC: rpcrdma_register_default_external: Dynamically allocate ib_phys_buf

On Mon, Mar 11, 2013 at 12:51:44PM -0600, Tim Gardner wrote:

On 03/11/2013 12:14 PM, J. Bruce Fields wrote:
<snip>

quoted

quoted

v2 - Move the array of 'struct ib_phys_buf' objects into struct rpcrdma_req
and pass this request down through rpcrdma_register_external() and
rpcrdma_register_default_external(). This is less overhead then using
kmalloc() and requires no extra error checking as the allocation burden is
shifted to the transport client.

Oh good--so that works, and the req is the right place to put this?  How
are you testing this?

(Just want to make it clear: I'm *not* an expert on the rdma code, so my
suggestion to put this in the rpcrdma_req was a suggestion for something
to look into, not a claim that it's correct.)

Just compile tested so far. Incidentally, I've been through the call stack:

call_transmit
 xprt_transmit
  xprt->ops->send_request(task)
   xprt_rdma_send_request
    rpcrdma_marshal_req
     rpcrdma_create_chunks
      rpcrdma_register_external
       rpcrdma_register_default_external

It appears that the context for kmalloc() should be fine unless there is
a spinlock held around call_transmit() (which seems unlikely).

Right, though I think it shouldn't be GFP_KERNEL--looks like writes
could wait on it.

In any case, the embedding-in-rpcrdma_req solution does look cleaner if
that's correct (e.g. if we can be sure there won't be two simultaneous
users of that array).

--b.