Re: [PATCH] xprtrdma: make sure MRs are unmapped before freeing them

[Dan Aloni <dan@kernelim.com>]

On Fri, Aug 14, 2020 at 02:12:48PM -0400, Chuck Lever wrote:
> Hi Dan-
> 
> > On Aug 14, 2020, at 1:37 PM, Dan Aloni <dan@kernelim.com> wrote:
> > 
> > It was observed that on disconnections, these unmaps don't occur. The
> > relevant path is rpcrdma_mrs_destroy(), being called from
> > rpcrdma_xprt_disconnect().
> 
> MRs are supposed to be unmapped right after they are used, so
> during disconnect they should all be unmapped already. How often
> do you see a DMA mapped MR in this code path? Do you have a
> reproducer I can try?

These are not graceful disconnections but abnormal ones, where many large
IOs are still in flight, while the remote server suddenly breaks the
connection, the remote IP is still reachable but refusing to accept new
connections only for a few seconds.

We may also need reconnection attempts in the background trying to
recover the xprt, so that with short reconnect timeouts it may be enough
for xprt_rdma_close() to be triggered from xprt_rdma_connect_worker(),
leading up to rpcrdma_xprt_disconnect().

-- 
Dan Aloni