From a55090db2ac16aa2ee9d25940e11ca5467af661b Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Tue, 14 Jan 2025 18:07:32 -0500 Subject: [PATCH] migration: Do not construct JSON description if suppressed QEMU machine has a property "suppress-vmdesc". When it is enabled, QEMU will stop attaching JSON VM description at the end of the precopy migration stream (postcopy is never affected because postcopy never attach that). However even if it's suppressed by the user, the source QEMU will still construct the JSON descriptions, which is a complete waste of CPU and memory resources. To avoid it, only create the JSON writer object if suppress-vmdesc is not specified. Luckily, vmstate_save() already supports vmdesc==NULL, so only a few spots that are left to be prepared that vmdesc can be NULL now. When at it, move the init / destroy of the JSON writer object to start / end of the migration - the JSON writer object is a sub-struct of migration state, and that looks like the only object that was dynamically allocated / destroyed within migration process. Make it the same as the rest objects that migration uses. Signed-off-by: Peter Xu Tested-by: Jiri Denemark Reviewed-by: Juraj Marcin Link: https://lore.kernel.org/r/20250114230746.3268797-3-peterx@redhat.com Signed-off-by: Fabiano Rosas --- migration/migration.c | 9 +++++--- migration/migration.h | 1 + migration/savevm.c | 49 +++++++++++++++++++++++-------------------- 3 files changed, 33 insertions(+), 26 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index 88b09914ec..5c335cc30b 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -1431,8 +1431,8 @@ static void migrate_fd_cleanup(MigrationState *s) g_free(s->hostname); s->hostname = NULL; - json_writer_free(s->vmdesc); - s->vmdesc = NULL; + + g_clear_pointer(&s->vmdesc, json_writer_free); qemu_savevm_state_cleanup(); cpr_state_close(); @@ -1722,7 +1722,10 @@ int migrate_init(MigrationState *s, Error **errp) s->migration_thread_running = false; error_free(s->error); s->error = NULL; - s->vmdesc = NULL; + + if (should_send_vmdesc()) { + s->vmdesc = json_writer_new(false); + } migrate_set_state(&s->state, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP); diff --git a/migration/migration.h b/migration/migration.h index fb1b8f99d3..4c1fafc2b5 100644 --- a/migration/migration.h +++ b/migration/migration.h @@ -552,6 +552,7 @@ void migration_bitmap_sync_precopy(bool last_stage); /* migration/block-dirty-bitmap.c */ void dirty_bitmap_mig_init(void); +bool should_send_vmdesc(void); /* migration/block-active.c */ void migration_block_active_setup(bool active); diff --git a/migration/savevm.c b/migration/savevm.c index b8859d367f..cfe9dfaf5c 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -1231,8 +1231,7 @@ void qemu_savevm_non_migratable_list(strList **reasons) void qemu_savevm_state_header(QEMUFile *f) { MigrationState *s = migrate_get_current(); - - s->vmdesc = json_writer_new(false); + JSONWriter *vmdesc = s->vmdesc; trace_savevm_state_header(); qemu_put_be32(f, QEMU_VM_FILE_MAGIC); @@ -1241,16 +1240,21 @@ void qemu_savevm_state_header(QEMUFile *f) if (s->send_configuration) { qemu_put_byte(f, QEMU_VM_CONFIGURATION); - /* - * This starts the main json object and is paired with the - * json_writer_end_object in - * qemu_savevm_state_complete_precopy_non_iterable - */ - json_writer_start_object(s->vmdesc, NULL); + if (vmdesc) { + /* + * This starts the main json object and is paired with the + * json_writer_end_object in + * qemu_savevm_state_complete_precopy_non_iterable + */ + json_writer_start_object(vmdesc, NULL); + json_writer_start_object(vmdesc, "configuration"); + } + + vmstate_save_state(f, &vmstate_configuration, &savevm_state, vmdesc); - json_writer_start_object(s->vmdesc, "configuration"); - vmstate_save_state(f, &vmstate_configuration, &savevm_state, s->vmdesc); - json_writer_end_object(s->vmdesc); + if (vmdesc) { + json_writer_end_object(vmdesc); + } } } @@ -1296,16 +1300,19 @@ int qemu_savevm_state_setup(QEMUFile *f, Error **errp) { ERRP_GUARD(); MigrationState *ms = migrate_get_current(); + JSONWriter *vmdesc = ms->vmdesc; SaveStateEntry *se; int ret = 0; - json_writer_int64(ms->vmdesc, "page_size", qemu_target_page_size()); - json_writer_start_array(ms->vmdesc, "devices"); + if (vmdesc) { + json_writer_int64(vmdesc, "page_size", qemu_target_page_size()); + json_writer_start_array(vmdesc, "devices"); + } trace_savevm_state_setup(); QTAILQ_FOREACH(se, &savevm_state.handlers, entry) { if (se->vmsd && se->vmsd->early_setup) { - ret = vmstate_save(f, se, ms->vmdesc, errp); + ret = vmstate_save(f, se, vmdesc, errp); if (ret) { migrate_set_error(ms, *errp); qemu_file_set_error(f, ret); @@ -1424,7 +1431,7 @@ int qemu_savevm_state_iterate(QEMUFile *f, bool postcopy) return all_finished; } -static bool should_send_vmdesc(void) +bool should_send_vmdesc(void) { MachineState *machine = MACHINE(qdev_get_machine()); @@ -1564,21 +1571,17 @@ int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f, /* Postcopy stream will still be going */ qemu_put_byte(f, QEMU_VM_EOF); - json_writer_end_array(vmdesc); - json_writer_end_object(vmdesc); - vmdesc_len = strlen(json_writer_get(vmdesc)); + if (vmdesc) { + json_writer_end_array(vmdesc); + json_writer_end_object(vmdesc); + vmdesc_len = strlen(json_writer_get(vmdesc)); - if (should_send_vmdesc()) { qemu_put_byte(f, QEMU_VM_VMDESCRIPTION); qemu_put_be32(f, vmdesc_len); qemu_put_buffer(f, (uint8_t *)json_writer_get(vmdesc), vmdesc_len); } } - /* Free it now to detect any inconsistencies. */ - json_writer_free(vmdesc); - ms->vmdesc = NULL; - trace_vmstate_downtime_checkpoint("src-non-iterable-saved"); return 0; -- 2.30.2