| Message ID | 20210106152120.31279-1-andrey.gruzdev@virtuozzo.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | UFFD write-tracking migration/snapshots | expand |
Ping On 06.01.2021 18:21, Andrey Gruzdev 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. > > How to use: > 1. Enable write-tracking migration capability > virsh qemu-monitor-command <domain> --hmp migrate_set_capability. > track-writes-ram 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 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 | 365 ++++++++++++++++++++++++++++++++++- > migration/migration.h | 4 + > migration/ram.c | 288 ++++++++++++++++++++++++++- > migration/ram.h | 6 + > migration/savevm.c | 1 - > migration/savevm.h | 2 + > migration/trace-events | 2 + > qapi/migration.json | 7 +- > scripts/userfaultfd-wrlat.py | 148 ++++++++++++++ > util/meson.build | 1 + > util/trace-events | 9 + > util/userfaultfd.c | 345 +++++++++++++++++++++++++++++++++ > 14 files changed, 1211 insertions(+), 10 deletions(-) > create mode 100644 include/qemu/userfaultfd.h > create mode 100755 scripts/userfaultfd-wrlat.py > create mode 100644 util/userfaultfd.c >
On Fri, Jan 15, 2021 at 02:34:40PM +0300, Andrey Gruzdev wrote:
> Ping
Dave, Juan,
I really think this series needs some attention...
It'll be a great if QEMU can start to take live snapshot at least to me.
Andrey (and also Denis with the older versions) did a great job working on it
and moving it forward. IMHO it's something beneficial for the QEMU community
and we should really encourage such behavior on working useful things, working
in collaborative way, and being consistent.
Is there any concern about this series? Let me know if there's anything I can
help with it.
Thanks!