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

From: Fabiano Rosas <farosas@suse.de>
To: Peter Xu <peterx@redhat.com>, Hao Xiang <hao.xiang@bytedance.com>
Cc: pbonzini@redhat.com, berrange@redhat.com, eduardo@habkost.net,
	eblake@redhat.com, armbru@redhat.com, thuth@redhat.com,
	lvivier@redhat.com, jdenemar@redhat.com,
	marcel.apfelbaum@gmail.com, philmd@linaro.org,
	wangyanan55@huawei.com, qemu-devel@nongnu.org
Subject: Re: [PATCH v4 2/7] migration/multifd: Implement zero page transmission on the multifd thread.
Date: Mon, 04 Mar 2024 15:24:05 -0300	[thread overview]
Message-ID: <87r0gp97p6.fsf@suse.de> (raw)
In-Reply-To: <878r2ynnky.fsf@suse.de>

Fabiano Rosas <farosas@suse.de> writes:

> 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.

@Hao Xiang:

Here's a branch with the rebase. Please include the first two commits
when you repost:

 migration/multifd: Allow clearing of the file_bmap from multifd
 migration/multifd: Allow zero pages in file migration

There are also two small additions and some conflict resolution at the
"Implement zero page..." commit. Make sure you don't miss them.

https://gitlab.com/farosas/qemu/-/commits/migration-multifd-zero-page

Let me know if you encounter any issues.