Re: [Qemu-devel] [RFC Design Doc]Speed up live migration by skipping free pages

[Wei Yang <richard.weiyang@huawei.com>]

On Wed, Mar 23, 2016 at 06:48:22AM +0000, Li, Liang Z wrote:
[...]
>> > 8. Pseudo code
>> > Dirty page logging should be enabled before getting the free page
>> > information from guest, this is important because during the process
>> > of getting free pages, some free pages may be used and written by the
>> > guest, dirty page logging can trace these pages. The pseudo code is
>> > like below:
>> >
>> >     -----------------------------------------------
>> >     MigrationState *s = migrate_get_current();
>> >     ...
>> >
>> >     memory_global_dirty_log_start();
>> >
>> >     if (get_guest_mem_info(&info)) {
>> >         while (!get_free_page_bmap(free_page_bitmap,  drop_page_cache)
>> &&
>> >                s->state != MIGRATION_STATUS_CANCELLING) {
>> >             usleep(1000) // sleep for 1 ms
>> >         }
>> >
>> >         tighten_free_page_bmap =
>> tighten_guest_free_pages(free_page_bitmap);
>> >         filter_out_guest_free_pages(tighten_free_page_bmap);
>> >     }
>> 
>> Given the typical speed of networks; it wouldn't do too much harm to start
>> sending assuming all pages are dirty and then when the guest finally gets
>> around to finishing the bitmap then update, so it's asynchronous - and then if
>> the guest never responds we don't really care.
>
>Indeed, thanks!
>

This is interesting. By doing so, the threshold I mentioned in another mail is
not necessary, since we can do it in parallel.

>Liang
>> 
>> Dave
>> 
>> >
>> >     migration_bitmap_sync();
>> >     ...
>> >
>> >     -----------------------------------------------
>> >
>> >
>> > --
>> > 1.9.1
>> >
>> --
>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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-- 
Richard Yang\nHelp you, Help me