Intro ===== This patch series implements postcopy live migration.[1] As discussed at KVM forum 2011, dedicated character device is used for distributed shared memory between migration source and destination. Now we can discuss/benchmark/compare with precopy. I believe there are much rooms for improvement. [1] http://wiki.qemu.org/Features/PostCopyLiveMigration Usage ===== You need load umem character device on the host before starting migration. Postcopy can be used for tcg and kvm accelarator. The implementation depend on only linux umem character device. But the driver dependent code is split into a file. I tested only host page size == guest page size case, but the implementation allows host page size != guest page size case. The following options are added with this patch series. - incoming part command line options -postcopy [-postcopy-flags <flags>] where flags is for changing behavior for benchmark/debugging Currently the following flags are available 0: default 1: enable touching page request example: qemu -postcopy -incoming tcp:0:4444 -monitor stdio -machine accel=kvm - outging part options for migrate command migrate [-p [-n]] URI -p: indicate postcopy migration -n: disable background transferring pages: This is for benchmark/debugging example: migrate -p -n tcp:<dest ip address>:4444 TODO ==== - benchmark/evaluation. Especially how async page fault affects the result. - improve/optimization At the moment at least what I'm aware of is - touching pages in incoming qemu process by fd handler seems suboptimal. creating dedicated thread? - making incoming socket non-blocking - outgoing handler seems suboptimal causing latency. - catch up memory API change - consider on FUSE/CUSE possibility - and more... basic postcopy work flow ======================== qemu on the destination | V open(/dev/umem) | V UMEM_DEV_CREATE_UMEM | V Here we have two file descriptors to umem device and shmem file | | umemd | daemon on the destination | V create pipe to communicate fork()---------------------------------------, | | V | close(socket) V close(shmem) mmap(shmem file) | | V V mmap(umem device) for guest RAM close(shmem file) | | close(umem device) | | | V | wait for ready from daemon <----pipe-----send ready message | | | Here the daemon takes over send ok------------pipe---------------> the owner of the socket | to the source V | entering post copy stage | start guest execution | | | V V access guest RAM UMEM_GET_PAGE_REQUEST | | V V page fault ------------------------------>page offset is returned block | V pull page from the source write the page contents to the shmem. | V unblock <-----------------------------UMEM_MARK_PAGE_CACHED the fault handler returns the page page fault is resolved | | pages can be sent | backgroundly | | | V | UMEM_MARK_PAGE_CACHED | | V V The specified pages<-----pipe------------request to touch pages are made present by | touching guest RAM. | | | V V reply-------------pipe-------------> release the cached page | madvise(MADV_REMOVE) | | V V all the pages are pulled from the source | | V V the vma becomes anonymous<----------------UMEM_MAKE_VMA_ANONYMOUS (note: I'm not sure if this can be implemented or not) | | V V migration completes exit() Isaku Yamahata (21): arch_init: export sort_ram_list() and ram_save_block() arch_init: export RAM_SAVE_xxx flags for postcopy arch_init/ram_save: introduce constant for ram save version = 4 arch_init: refactor host_from_stream_offset() arch_init/ram_save_live: factor out RAM_SAVE_FLAG_MEM_SIZE case arch_init: refactor ram_save_block() arch_init/ram_save_live: factor out ram_save_limit arch_init/ram_load: refactor ram_load exec.c: factor out qemu_get_ram_ptr() exec.c: export last_ram_offset() savevm: export qemu_peek_buffer, qemu_peek_byte, qemu_file_skip savevm: qemu_pending_size() to return pending buffered size savevm, buffered_file: introduce method to drain buffer of buffered file migration: export migrate_fd_completed() and migrate_fd_cleanup() migration: factor out parameters into MigrationParams umem.h: import Linux umem.h update-linux-headers.sh: teach umem.h to update-linux-headers.sh configure: add CONFIG_POSTCOPY option postcopy: introduce -postcopy and -postcopy-flags option postcopy outgoing: add -p and -n option to migrate command postcopy: implement postcopy livemigration Makefile.target | 4 + arch_init.c | 260 ++++--- arch_init.h | 20 + block-migration.c | 8 +- buffered_file.c | 20 +- buffered_file.h | 1 + configure | 12 + cpu-all.h | 9 + exec-obsolete.h | 1 + exec.c | 75 +- hmp-commands.hx | 12 +- hw/hw.h | 7 +- linux-headers/linux/umem.h | 83 ++ migration-exec.c | 8 + migration-fd.c | 30 + migration-postcopy-stub.c | 77 ++ migration-postcopy.c | 1891 +++++++++++++++++++++++++++++++++++++++ migration-tcp.c | 37 +- migration-unix.c | 32 +- migration.c | 53 +- migration.h | 49 +- qemu-common.h | 2 + qemu-options.hx | 25 + qmp-commands.hx | 10 +- savevm.c | 31 +- scripts/update-linux-headers.sh | 2 +- sysemu.h | 4 +- umem.c | 379 ++++++++ umem.h | 105 +++ vl.c | 20 +- 30 files changed, 3086 insertions(+), 181 deletions(-) create mode 100644 linux-headers/linux/umem.h create mode 100644 migration-postcopy-stub.c create mode 100644 migration-postcopy.c create mode 100644 umem.c create mode 100644 umem.h -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
