On Mon, Mar 11, 2013 at 07:48:51PM +0000, Myklebust, Trond wrote: > On Mon, 2013-03-11 at 15:15 -0400, J. Bruce Fields wrote: > > 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> > > > >> > > > >> 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. > > Nothing inside the RPC client should be using anything heavier than > GFP_NOWAIT (unless done at setup). > > > 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). > > Putting it in the rpcrdma_req means that you have one copy per transport > slot. Why not rather put it in the rpcrdma_xprt? > AFAICS you only need this array at transmit time for registering memory > for RDMA, at which time the transport XPRT_LOCK guarantees that nobody > else is competing for these resources. Oh, good. If that works, Steve might want to look back at how that array size was chosen? I seem to recall there being some compromise due to this array being on the stack, and that there might have been some performance advantage to increasing it further, but I can't find the bug right now.... (And I might be misremembering.) --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
