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envelope-from=andrey.gruzdev@virtuozzo.com; helo=EUR04-VI1-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 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" On 28.11.2020 01:04, Peter Xu wrote: > On Thu, Nov 26, 2020 at 06:17:28PM +0300, Andrey Gruzdev wrote: >> Changes v3->v4: >> >> * 1. Renamed migrate capability 'track-writes-ram'->'background-snapshot'. >> * 2. Use array of incompatible caps to replace bulky 'if' constructs. >> * 3. Moved UFFD low-level code to the separate module ('util/userfaultfd.c'). >> * 4. Always do UFFD wr-unprotect on cleanup; just closing file descriptor >> * won't cleanup PTEs anyhow, it will release registration ranges, wait >> * queues etc. but won't cleanup process MM context on MMU level. >> * 5. Allow to enable 'background-snapshot' capability on Linux-only hosts. >> * 6. Put UFFD code usage under '#ifdef CONFIG_LINUX' prerequisite. >> * 7. Removed 'wt_' from RAMState struct. >> * 8. Refactored ram_find_and_save_block() to make more clean - poll UFFD >> * wr-fault events in get_queued_page(), use ram_save_host_page_pre(), >> * ram_save_host_page_post() notifiers around ram_save_host_page() >> * instead of bulky inline write-unprotect code. > > One thing I mentioned previously but it seems still got lost is that we don't > need dirty tracking for live snapshot. > > A few pointers for reference: > > memory_global_dirty_log_start() > migration_bitmap_sync_precopy() > memory_region_clear_dirty_bitmap() > ... > > These should not be needed. But this can also be done on top. > > Thanks, > Yes, all off this is really not needed. At least it seems that enabled dirty page logging in KVM makes not too much overhead and migration_bitmap_sync_precopy() is called only once. Let's do it on top. -- Andrey Gruzdev, Principal Engineer Virtuozzo GmbH +7-903-247-6397 virtuzzo.com