xprtrdma: ->send_request returns -EAGAIN when there are no free MRs

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Currently, when the MR free list is exhausted during marshaling, the
RPC/RDMA transport places the RPC task on the delayq, which forces a
wait for HZ >> 2 before the marshal and send is retried.

With this change, the transport now places such an RPC task on the
pending queue, and wakes it just as soon as more MRs have been
created. Creating more MRs typically takes less than a millisecond,
and this waking mechanism is less deadlock-prone.

Moreover, the waiting RPC task is holding the transport's write
lock, which blocks the transport from sending RPCs. Therefore faster
recovery from MR exhaustion is desirable.

This is the same mechanism that the TCP transport utilizes when
handling write buffer space exhaustion.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

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This commit is contained in:

Chuck Lever 2018-02-28 15:30:44 -05:00 • committed by Anna Schumaker

parent 8a14793e7a

commit 9e679d5e76

5 changed files with 27 additions and 13 deletions

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2

net/sunrpc/xprtrdma/fmr_ops.c

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net/sunrpc/xprtrdma/frwr_ops.c

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30

net/sunrpc/xprtrdma/rpc_rdma.c

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net/sunrpc/xprtrdma/transport.c

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3

net/sunrpc/xprtrdma/verbs.c

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