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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Jun 07, 2021 at 01:57:02PM +0000, LIZHAOXIN1 [李照鑫] wrote:
> 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) {

'pc.ram' is an x86 architecture specific name, so this will still
leave a problem on other architectures I assume.

> +            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;

Regards,
Daniel
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