[PATCH] migration/rdma: Use huge page register VM memory

[LIZHAOXIN1 [李照鑫]]

When using libvirt for RDMA live migration, if the VM memory is too large,
it will take a lot of time to deregister the VM at the source side, resulting
in a long downtime (VM 64G, deregister vm time is about 400ms).
    
Although the VM's memory uses 2M huge pages, the MLNX driver still uses 4K
pages for pin memory, as well as for unpin. So we use huge pages to skip the
process of pin memory and unpin memory to reduce downtime.
   
The test environment:
kernel: linux-5.12
MLNX: ConnectX-4 LX
libvirt command:
virsh migrate --live --p2p --persistent --copy-storage-inc --listen-address \
0.0.0.0 --rdma-pin-all --migrateuri rdma://192.168.0.2 [VM] 
qemu+tcp://192.168.0.2/system
    
Signed-off-by: lizhaoxin <lizhaoxin1@kingsoft.com>

diff --git a/migration/rdma.c b/migration/rdma.c
index 1cdb4561f3..9823449297 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -1123,13 +1123,26 @@ static int qemu_rdma_reg_whole_ram_blocks(RDMAContext 
*rdma)
     RDMALocalBlocks *local = &rdma->local_ram_blocks;
 
     for (i = 0; i < local->nb_blocks; i++) {
-        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
-                    );
+        if (strcmp(local->block[i].block_name,"pc.ram") == 0) {
+            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 |
+                        IBV_ACCESS_ON_DEMAND |
+                        IBV_ACCESS_HUGETLB
+                        );
+        } else {
+            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
+                        );
+        }
+
         if (!local->block[i].mr) {
             perror("Failed to register local dest ram block!\n");
             break;