[PATCH 1/2] migration/rdma: Try to register On-Demand Paging memory region

[Li Zhijian]

Previously, for the fsdax mem-backend-file, it will register failed with
Operation not supported. In this case, we can try to register it with
On-Demand Paging[1] like what rpma_mr_reg() does on rpma[2].

[1]: 
https://community.mellanox.com/s/article/understanding-on-demand-paging--odp-x
[2]: http://pmem.io/rpma/manpages/v0.9.0/rpma_mr_reg.3
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
---
 migration/rdma.c       | 27 ++++++++++++++++++---------
 migration/trace-events |  1 +
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/migration/rdma.c b/migration/rdma.c
index 5c2d113aa94..8784b5f22a6 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -1123,15 +1123,21 @@ static int qemu_rdma_reg_whole_ram_blocks(RDMAContext 
*rdma)
     RDMALocalBlocks *local = &rdma->local_ram_blocks;
 
     for (i = 0; i < local->nb_blocks; i++) {
+        int access = IBV_ACCESS_LOCAL_WRITE | IBV_ACCESS_REMOTE_WRITE;
+
+on_demand:
         local->block[i].mr =
             ibv_reg_mr(rdma->pd,
                     local->block[i].local_host_addr,
-                    local->block[i].length,
-                    IBV_ACCESS_LOCAL_WRITE |
-                    IBV_ACCESS_REMOTE_WRITE
+                    local->block[i].length, access
                     );
         if (!local->block[i].mr) {
-            perror("Failed to register local dest ram block!");
+            if (!(access & IBV_ACCESS_ON_DEMAND) && errno == ENOTSUP) {
+                access |= IBV_ACCESS_ON_DEMAND;
+                trace_qemu_rdma_register_odp_mr(local->block[i].block_name);
+                goto on_demand;
+            }
+            perror("Failed to register local dest ram block!\n");
             break;
         }
         rdma->total_registrations++;
@@ -1215,15 +1221,18 @@ static int qemu_rdma_register_and_get_keys(RDMAContext 
*rdma,
      */
     if (!block->pmr[chunk]) {
         uint64_t len = chunk_end - chunk_start;
+        int access = rkey ? IBV_ACCESS_LOCAL_WRITE | IBV_ACCESS_REMOTE_WRITE : 
0;
 
         trace_qemu_rdma_register_and_get_keys(len, chunk_start);
 
-        block->pmr[chunk] = ibv_reg_mr(rdma->pd,
-                chunk_start, len,
-                (rkey ? (IBV_ACCESS_LOCAL_WRITE |
-                        IBV_ACCESS_REMOTE_WRITE) : 0));
-
+on_demand:
+        block->pmr[chunk] = ibv_reg_mr(rdma->pd, chunk_start, len, access);
         if (!block->pmr[chunk]) {
+            if (!(access & IBV_ACCESS_ON_DEMAND) && errno == ENOTSUP) {
+                access |= IBV_ACCESS_ON_DEMAND;
+                trace_qemu_rdma_register_odp_mr(block->block_name);
+                goto on_demand;
+            }
             perror("Failed to register chunk!");
             fprintf(stderr, "Chunk details: block: %d chunk index %d"
                             " start %" PRIuPTR " end %" PRIuPTR
diff --git a/migration/trace-events b/migration/trace-events
index a1c0f034ab8..5f6aa580def 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -212,6 +212,7 @@ qemu_rdma_poll_write(const char *compstr, int64_t comp, int 
left, uint64_t block
 qemu_rdma_poll_other(const char *compstr, int64_t comp, int left) "other 
completion %s (%" PRId64 ") received left %d"
 qemu_rdma_post_send_control(const char *desc) "CONTROL: sending %s.."
 qemu_rdma_register_and_get_keys(uint64_t len, void *start) "Registering %" 
PRIu64 " bytes @ %p"
+qemu_rdma_register_odp_mr(const char *name) "Try to register On-Demand Paging 
memory region: %s"
 qemu_rdma_registration_handle_compress(int64_t length, int index, int64_t 
offset) "Zapping zero chunk: %" PRId64 " bytes, index %d, offset %" PRId64
 qemu_rdma_registration_handle_finished(void) ""
 qemu_rdma_registration_handle_ram_blocks(void) ""
-- 
2.31.1