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

[LIZHAOXIN1 [李照鑫]]

Yes, When I configured two NUMAs for the VM, the name of the memory 
is 'ram-node*', and other architectures had different names.
As you suggested, I use qemu_ram_pagesize() and qemu_real_host_page_size 
to determine which Ramblocks use huge page.
I will send the patch second version later.

when there's a mix of different huge page sizes, there is no difference in 
their 
behavior, register or pin are just to prevent the memory from being swapped 
out. 
Huge page itself will not be swapped out，so huge page no need deregister or 
unpin.

The libvirt xml of my VM is 
...
<memoryBacking>
    <hugepages>
      <page size='2048' unit='KiB' nodeset='0'/>
      <page size='1048576' unit='KiB' nodeset='1'/>
    </hugepages>
  </memoryBacking>
...
<numa>
      <cell id='0' cpus='0-7' memory='31457280' unit='KiB' memAccess='shared'/>
      <cell id='1' cpus='8-15' memory='2097152' unit='KiB' memAccess='shared'/>
</numa>
...

After testing, the RDMA live migration is normal, and the downtime is 
significantly reduced.

-----邮件原件-----
发件人: Dr. David Alan Gilbert <dgilbert@redhat.com> 
发送时间: 2021年6月7日 23:00
收件人: Daniel P. Berrangé <berrange@redhat.com>
抄送: LIZHAOXIN1 [李照鑫] <LIZHAOXIN1@kingsoft.com>; qemu-devel@nongnu.org; 
quintela@redhat.com; sunhao2 [孙昊] <sunhao2@kingsoft.com>; DENGLINWEN [邓林文] 
<DENGLINWEN@kingsoft.com>; YANGFENG1 [杨峰] <YANGFENG1@kingsoft.com>
主题: Re: [PATCH] migration/rdma: Use huge page register VM memory

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> 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.

Yes, and also break even on PC when using NUMA.
I think the thing to do here is to call qemu_ram_pagesize on the RAMBlock; 

  if (qemu_ram_pagesize(RAMBlock....) != qemu_real_host_page_size)
     it's a huge page

I guess it's probably best to do that in qemu_rdma_init_one_block or something?

I wonder how that all works when there's a mix of different huge page sizes?

Dave

> > +            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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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK