Things have changed since this comment was written. In particular, the reworking of connection closing, on-demand creation of MRs, and the removal of fr_state all mean that deferring MR recovery to frwr_map is no longer needed. The description is obsolete. Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> --- net/sunrpc/xprtrdma/frwr_ops.c | 66 +++++++++++----------------------------- 1 file changed, 18 insertions(+), 48 deletions(-) diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c index 0b6dad7580a1..a30f2ae49578 100644 --- a/net/sunrpc/xprtrdma/frwr_ops.c +++ b/net/sunrpc/xprtrdma/frwr_ops.c @@ -7,67 +7,37 @@ /* Lightweight memory registration using Fast Registration Work * Requests (FRWR). * - * FRWR features ordered asynchronous registration and deregistration - * of arbitrarily sized memory regions. This is the fastest and safest + * FRWR features ordered asynchronous registration and invalidation + * of arbitrarily-sized memory regions. This is the fastest and safest * but most complex memory registration mode. */ /* Normal operation * - * A Memory Region is prepared for RDMA READ or WRITE using a FAST_REG + * A Memory Region is prepared for RDMA Read or Write using a FAST_REG * Work Request (frwr_map). When the RDMA operation is finished, this * Memory Region is invalidated using a LOCAL_INV Work Request - * (frwr_unmap_sync). + * (frwr_unmap_async and frwr_unmap_sync). * - * Typically these Work Requests are not signaled, and neither are RDMA - * SEND Work Requests (with the exception of signaling occasionally to - * prevent provider work queue overflows). This greatly reduces HCA + * Typically FAST_REG Work Requests are not signaled, and neither are + * RDMA Send Work Requests (with the exception of signaling occasionally + * to prevent provider work queue overflows). This greatly reduces HCA * interrupt workload. - * - * As an optimization, frwr_unmap marks MRs INVALID before the - * LOCAL_INV WR is posted. If posting succeeds, the MR is placed on - * rb_mrs immediately so that no work (like managing a linked list - * under a spinlock) is needed in the completion upcall. - * - * But this means that frwr_map() can occasionally encounter an MR - * that is INVALID but the LOCAL_INV WR has not completed. Work Queue - * ordering prevents a subsequent FAST_REG WR from executing against - * that MR while it is still being invalidated. */ /* Transport recovery * - * ->op_map and the transport connect worker cannot run at the same - * time, but ->op_unmap can fire while the transport connect worker - * is running. Thus MR recovery is handled in ->op_map, to guarantee - * that recovered MRs are owned by a sending RPC, and not one where - * ->op_unmap could fire at the same time transport reconnect is - * being done. - * - * When the underlying transport disconnects, MRs are left in one of - * four states: - * - * INVALID: The MR was not in use before the QP entered ERROR state. - * - * VALID: The MR was registered before the QP entered ERROR state. - * - * FLUSHED_FR: The MR was being registered when the QP entered ERROR - * state, and the pending WR was flushed. - * - * FLUSHED_LI: The MR was being invalidated when the QP entered ERROR - * state, and the pending WR was flushed. - * - * When frwr_map encounters FLUSHED and VALID MRs, they are recovered - * with ib_dereg_mr and then are re-initialized. Because MR recovery - * allocates fresh resources, it is deferred to a workqueue, and the - * recovered MRs are placed back on the rb_mrs list when recovery is - * complete. frwr_map allocates another MR for the current RPC while - * the broken MR is reset. - * - * To ensure that frwr_map doesn't encounter an MR that is marked - * INVALID but that is about to be flushed due to a previous transport - * disconnect, the transport connect worker attempts to drain all - * pending send queue WRs before the transport is reconnected. + * frwr_map and frwr_unmap_* cannot run at the same time the transport + * connect worker is running. The connect worker holds the transport + * send lock, just as ->send_request does. This prevents frwr_map and + * the connect worker from running concurrently. When a connection is + * closed, the Receive completion queue is drained before the allowing + * the connect worker to get control. This prevents frwr_unmap and the + * connect worker from running concurrently. + * + * When the underlying transport disconnects, MRs that are in flight + * are flushed and are likely unusable. Thus all flushed MRs are + * destroyed. New MRs are created on demand. */ #include <linux/sunrpc/rpc_rdma.h>
