* Dr. David Alan Gilbert (dgilb...@redhat.com) wrote: > * Andrey Gruzdev (andrey.gruz...@virtuozzo.com) wrote: > > This patch series is a kind of 'rethinking' of Denis Plotnikov's ideas he's > > implemented in his series '[PATCH v0 0/4] migration: add background > > snapshot'. > > > > Currently the only way to make (external) live VM snapshot is using existing > > dirty page logging migration mechanism. The main problem is that it tends to > > produce a lot of page duplicates while running VM goes on updating already > > saved pages. That leads to the fact that vmstate image size is commonly > > several > > times bigger then non-zero part of virtual machine's RSS. Time required to > > converge RAM migration and the size of snapshot image severely depend on the > > guest memory write rate, sometimes resulting in unacceptably long snapshot > > creation time and huge image size. > > > > This series propose a way to solve the aforementioned problems. This is done > > by using different RAM migration mechanism based on UFFD write protection > > management introduced in v5.7 kernel. The migration strategy is to 'freeze' > > guest RAM content using write-protection and iteratively release protection > > for memory ranges that have already been saved to the migration stream. > > At the same time we read in pending UFFD write fault events and save those > > pages out-of-order with higher priority. > > Queued > Andrey: I've fixed up some 32bit build casts in the pull. Please check them.
Dave > > How to use: > > 1. Enable write-tracking migration capability > > virsh qemu-monitor-command <domain> --hmp migrate_set_capability > > background-snapshot on > > > > 2. Start the external migration to a file > > virsh qemu-monitor-command <domain> --hmp migrate exec:'cat > ./vm_state' > > > > 3. Wait for the migration finish and check that the migration has completed. > > state. > > > > > > Changes v13->v14: > > > > * 1. Removed unneeded '#ifdef CONFIG_LINUX' from [PATCH 1/5] where #ifdef'ed > > * code was originally introduced. In v13 removed #ifdef's appeared to be > > * a diff in [PATCH 4/5] on top of previous patches. > > > > Changes v12->v13: > > > > * 1. Fixed codestyle problem for checkpatch. > > > > Changes v11->v12: > > > > * 1. Consolidated UFFD-related code under single #if defined(__linux__). > > * 2. Abandoned use of pre/post hooks in ram_find_and_save_block() in favour > > * of more compact code fragment in ram_save_host_page(). > > * 3. Refactored/simplified eBPF code in userfaultfd-wrlat.py script. > > > > Changes v10->v11: > > > > * 1. Updated commit messages. > > > > Changes v9->v10: > > > > * 1. Fixed commit message for [PATCH v9 1/5]. > > > > Changes v8->v9: > > > > * 1. Fixed wrong cover letter subject. > > > > Changes v7->v8: > > > > * 1. Fixed coding style problems to pass checkpatch. > > > > Changes v6->v7: > > > > * 1. Fixed background snapshot on suspended guest: call > > qemu_system_wakeup_request() > > * before stopping VM to make runstate transition valid. > > * 2. Disabled dirty page logging and log syn when 'background-snapshot' is > > enabled. > > * 3. Introduced 'userfaultfd-wrlat.py' script to analyze UFFD write fault > > latencies. > > > > Changes v5->v6: > > > > * 1. Consider possible hot pluggin/unpluggin of memory device - don't use > > static > > * for write-tracking support level in migrate_query_write_tracking(), > > check > > * each time when one tries to enable 'background-snapshot' capability. > > > > Changes v4->v5: > > > > * 1. Refactored util/userfaultfd.c code to support features required by > > postcopy. > > * 2. Introduced checks for host kernel and guest memory backend > > compatibility > > * to 'background-snapshot' branch in migrate_caps_check(). > > * 3. Switched to using trace_xxx instead of info_report()/error_report() for > > * cases when error message must be hidden (probing UFFD-IO) or info may > > be > > * really littering output if goes to stderr. > > * 4 Added RCU_READ_LOCK_GUARDs to the code dealing with RAM block list. > > * 5. Added memory_region_ref() for each RAM block being wr-protected. > > * 6. Reused qemu_ram_block_from_host() instead of custom RAM block lookup > > routine. > > * 7. Refused from using specific hwaddr/ram_addr_t in favour of void > > */uint64_t. > > * 8. Currently dropped 'linear-scan-rate-limiting' patch. The reason is that > > * that choosen criteria for high-latency fault detection (i.e. timestamp > > of > > * UFFD event fetch) is not representative enough for this task. > > * At the moment it looks somehow like premature optimization effort. > > * 8. Dropped some unnecessary/unused code. > > > > Andrey Gruzdev (5): > > migration: introduce 'background-snapshot' migration capability > > migration: introduce UFFD-WP low-level interface helpers > > migration: support UFFD write fault processing in ram_save_iterate() > > migration: implementation of background snapshot thread > > migration: introduce 'userfaultfd-wrlat.py' script > > > > include/exec/memory.h | 8 + > > include/qemu/userfaultfd.h | 35 ++++ > > migration/migration.c | 357 ++++++++++++++++++++++++++++++++++- > > migration/migration.h | 4 + > > migration/ram.c | 303 ++++++++++++++++++++++++++++- > > migration/ram.h | 6 + > > migration/savevm.c | 1 - > > migration/savevm.h | 2 + > > migration/trace-events | 2 + > > qapi/migration.json | 7 +- > > scripts/userfaultfd-wrlat.py | 122 ++++++++++++ > > util/meson.build | 1 + > > util/trace-events | 9 + > > util/userfaultfd.c | 345 +++++++++++++++++++++++++++++++++ > > 14 files changed, 1190 insertions(+), 12 deletions(-) > > create mode 100644 include/qemu/userfaultfd.h > > create mode 100755 scripts/userfaultfd-wrlat.py > > create mode 100644 util/userfaultfd.c > > > > -- > > 2.25.1 > > > > > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
