Re: [PATCH v4 2/7] migration/multifd: Implement zero page transmission on the multifd thread.

[Fabiano Rosas]

Peter Xu <peterx@redhat.com> writes:

> On Fri, Mar 01, 2024 at 02:28:24AM +0000, Hao Xiang wrote:
>> -GlobalProperty hw_compat_8_2[] = {};
>> +GlobalProperty hw_compat_8_2[] = {
>> +    { "migration", "zero-page-detection", "legacy"},
>> +};
>
> I hope we can make it for 9.0, then this (and many rest places) can be kept
> as-is.  Let's see..  soft-freeze is March 12th.
>
> One thing to mention is I just sent a pull which has mapped-ram feature
> merged.  You may need a rebase onto that, and hopefully mapped-ram can also
> use your feature too within the same patch when you repost.

The key points are:

- The socket migration is under "use_packets", the mapped-ram is under
"!use_packets" always.

- mapped-ram doesn't trasmit zero-pages, it just clears the
corresponding bit in block->file_bmap.

> https://lore.kernel.org/all/20240229153017.2221-1-farosas@suse.de/
>
> That rebase may or may not need much caution, I apologize for that:
> mapped-ram as a feature was discussed 1+ years, so it was a plan to merge
> it (actually still partly of it) into QEMU 9.0.

I started doing that rebase last week and saw issues with a sender
thread always getting -EPIPE at the sendmsg() on the regular socket
migration. Let's hope it was just me being tired. I'll try to get
something ready this week.