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Berrange" , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH V2] migration: file URI In-Reply-To: References: <1686163139-256654-1-git-send-email-steven.sistare@oracle.com> <877cs6ujtu.fsf@suse.de> <874jn9vs9x.fsf@suse.de> Date: Thu, 15 Jun 2023 11:50:28 -0300 Message-ID: <87cz1wzsnf.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=2001:67c:2178:6::1d; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Xu 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+4QsDBtKR@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.