Peter Xu <pet...@redhat.com> writes: > On Wed, Jun 14, 2023 at 02:59:54PM -0300, Fabiano Rosas wrote: >> In this message Daniel mentions virDomainSnapshotXXX which would benefit >> from using the same "file" migration, but being done live: >> >> https://lore.kernel.org/r/zd7mrgq+4qsdb...@redhat.com >> >> And from your response here: >> https://lore.kernel.org/r/ZEA759BSs75ldW6Y@x1n >> >> I had understood that having a new SUSPEND cap to decide whether to do >> it live or non-live would be enough to cover all use-cases. > > Oh, I probably lost some of the contexts there, sorry about that - so it's > about not being able to live snapshot on !LINUX worlds properly, am I > right? >
Right, so that gives us for now a reasonable use-case for keeping live migration behavior possible with "file:". > In the ideal world where we can always synchronously tracking guest pages > (like what we do with userfaultfd wr-protections on modern Linux), the > !SUSPEND case should always be covered by CAP_BACKGROUND_SNAPSHOT already > in a more performant way. IOW, !SUSPEND seems to be not useful to Linux, > because whenever we want to set !SUSPEND we should just use BG_SNAPSHOT. > I agree. > But I think indeed the live snapshot support is not good enough. Even on > Linux, it lacks different memory type supports, multi-process support, and > also no-go on very old kernels. So I assume the fallback makes sense, and > then we can't always rely on that. > > Then I agree we can keep "file:" the same as others like proposed here, but > I'd like to double check with all of us so we're on the same page.. +1 > And maybe we should mention some discussions into commit message or > comments where proper in the code, so we can track what has happened > easier. > I'll add some words where appropriate in my series as well. A v2 is already overdue with all the refactorings that have happened in the migration code.