* Hailiang Zhang (zhang.zhanghaili...@huawei.com) wrote: > This patch will reduce the downtime of VM for the initial process, > Privously, we copied all these memory in preparing stage of COLO > while we need to stop VM, which is a time-consuming process. > Here we optimize it by a trick, back-up every page while in migration > process while COLO is enabled, though it affects the speed of the > migration, but it obviously reduce the downtime of back-up all SVM'S > memory in COLO preparing stage. > > Signed-off-by: Hailiang Zhang <zhang.zhanghaili...@huawei.com>
OK, I think this is right, but it took me quite a while to understand, I think one of the comments below might not be right: > --- > migration/colo.c | 3 +++ > migration/ram.c | 35 +++++++++++++++++++++++++++-------- > migration/ram.h | 1 + > 3 files changed, 31 insertions(+), 8 deletions(-) > > diff --git a/migration/colo.c b/migration/colo.c > index d30c6bc4ad..febf010571 100644 > --- a/migration/colo.c > +++ b/migration/colo.c > @@ -26,6 +26,7 @@ > #include "qemu/main-loop.h" > #include "qemu/rcu.h" > #include "migration/failover.h" > +#include "migration/ram.h" > #ifdef CONFIG_REPLICATION > #include "replication.h" > #endif > @@ -906,6 +907,8 @@ void *colo_process_incoming_thread(void *opaque) > */ > qemu_file_set_blocking(mis->from_src_file, true); > > + colo_incoming_start_dirty_log(); > + > bioc = qio_channel_buffer_new(COLO_BUFFER_BASE_SIZE); > fb = qemu_fopen_channel_input(QIO_CHANNEL(bioc)); > object_unref(OBJECT(bioc)); > diff --git a/migration/ram.c b/migration/ram.c > index ed23ed1c7c..24a8aa3527 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -2986,7 +2986,6 @@ int colo_init_ram_cache(void) > } > return -errno; > } > - memcpy(block->colo_cache, block->host, block->used_length); > } > } > > @@ -3005,12 +3004,16 @@ int colo_init_ram_cache(void) > bitmap_set(block->bmap, 0, pages); > } > } > + > + return 0; > +} > + > +void colo_incoming_start_dirty_log(void) > +{ > ram_state = g_new0(RAMState, 1); > ram_state->migration_dirty_pages = 0; > qemu_mutex_init(&ram_state->bitmap_mutex); > memory_global_dirty_log_start(); > - > - return 0; > } > > /* It is need to hold the global lock to call this helper */ > @@ -3348,7 +3351,7 @@ static int ram_load_precopy(QEMUFile *f) > > while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) { > ram_addr_t addr, total_ram_bytes; > - void *host = NULL; > + void *host = NULL, *host_bak = NULL; > uint8_t ch; > > /* > @@ -3378,13 +3381,26 @@ static int ram_load_precopy(QEMUFile *f) > if (flags & (RAM_SAVE_FLAG_ZERO | RAM_SAVE_FLAG_PAGE | > RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) { > RAMBlock *block = ram_block_from_stream(f, flags); > - > /* > - * After going into COLO, we should load the Page into > colo_cache. > + * After going into COLO, we should load the Page into colo_cache > + * NOTE: We need to keep a copy of SVM's ram in colo_cache. > + * Privously, we copied all these memory in preparing stage of > COLO > + * while we need to stop VM, which is a time-consuming process. > + * Here we optimize it by a trick, back-up every page while in > + * migration process while COLO is enabled, though it affects the > + * speed of the migration, but it obviously reduce the downtime > of > + * back-up all SVM'S memory in COLO preparing stage. > */ > - if (migration_incoming_in_colo_state()) { > + if (migration_incoming_colo_enabled()) { > host = colo_cache_from_block_offset(block, addr); > - } else { > + /* > + * After going into COLO, load the Page into colo_cache. > + */ > + if (!migration_incoming_in_colo_state()) { > + host_bak = host; > + } > + } > + if (!migration_incoming_in_colo_state()) { > host = host_from_ram_block_offset(block, addr); So this works out as quite complicated: a) In normal migration we do the last one and just set: host = host_from_ram_block_offset(block, addr); host_bak = NULL b) At the start, when colo_enabled, but !in_colo_state host = colo_cache host_bak = host host = host_from_ram_block_offset c) in_colo_state host = colo_cache host_bak = NULL (b) is pretty confusing, setting host twice; can't we tidy that up? Also, that last comment 'After going into COLO' I think is really 'Before COLO state, copy from ram into cache' Dave > } > if (!host) { > @@ -3506,6 +3522,9 @@ static int ram_load_precopy(QEMUFile *f) > if (!ret) { > ret = qemu_file_get_error(f); > } > + if (!ret && host_bak && host) { > + memcpy(host_bak, host, TARGET_PAGE_SIZE); > + } > } > > ret |= wait_for_decompress_done(); > diff --git a/migration/ram.h b/migration/ram.h > index a553d40751..5ceaff7cb4 100644 > --- a/migration/ram.h > +++ b/migration/ram.h > @@ -66,5 +66,6 @@ int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock > *rb); > /* ram cache */ > int colo_init_ram_cache(void); > void colo_release_ram_cache(void); > +void colo_incoming_start_dirty_log(void); > > #endif > -- > 2.21.0 > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK